Nanostructured materials for electrochemical conversion reactions

ABSTRACT

The disclosure is related to battery systems. More specifically, embodiments of the disclosure provide a nanostructured conversion material for use as the active material in battery cathodes. In an implementation, a nanostructured conversion material is a glassy material and includes a metal material, one or more oxidizing species, and a reducing cation species mixed at a scale of less than 1 nm. The glassy conversion material is substantially homogeneous within a volume of 1000 nm 3 .

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/922,214, filed on Jun. 19, 2013, entitled “NANOSTRUCTURED MATERIALSFOR ELECTROCHEMICAL CONVERSION REACTIONS”, which claims benefit of thefollowing U.S. Provisional Patent Applications under 35 U.S.C. 119(e):U.S. Provisional Patent Application No. 61/674,961, filed Jul. 24, 2012,and titled “NANOSCALE LITHIUM COMPOUND AND METAL ELECTRODES”; and U.S.Provisional Patent Application No. 61/814,821 filed Apr. 23, 2013, andtitled “NANOSTRUCTURED MATERIALS FOR ELECTROCHEMICAL CONVERSIONREACTIONS”, each of which is incorporated herein by reference in itsentirety and for all purposes.

BACKGROUND

The present disclosure is related to battery systems.

In the recent years, with shortage of fossil-fuel based energy andadverse environmental effects from the consumption of fossil fuel, bothpublic and private sectors have poured valuable resources into cleantechnologies. An important aspect of clean technologies is energystorage, or simply battery systems. Over the past, many battery typeshave been developed and used, with their respective advantages anddisadvantages. For its chemical properties, including high chargedensity, lithium material has been used in various parts of a battery.For example, in a rechargeable lithium-ion battery, lithium ions movefrom negative electrode to the positive electrode during discharge. Inthe basic operations of a lithium battery, a conversion materialundergoes a conversion reaction with lithium, and the performance of theconversion material is an important aspect of a battery.

Unfortunately, conventional battery systems and their manufacturing andprocesses result in relatively high cost, low energy density batteriesthat do not meet market demands for many applications. Therefore, it isdesirable to have new systems and techniques for batteries.

SUMMARY

One aspect of the disclosure concerns a positive electrode material thatmay be characterized by particles or nanodomains having a mediancharacteristic dimension of about 20 nm or less. These include (i)particles or nanodomains of a metal selected from the group consistingof iron, cobalt, manganese, copper, nickel, bismuth and alloys thereof,and (ii) particles or nanodomains of lithium fluoride.

In one implementation, the metal is iron, manganese or cobalt and themole ratio of metal to lithium fluoride is about 2 to 8. In anotherimplementation, the metal is copper or nickel and the mole ratio ofmetal to lithium fluoride is about 1 to 5. In certain embodiments, themetal is an alloy of iron with cobalt, copper, nickel and/or manganese.

In certain embodiments, the individual particles additionally include afluoride of the metal. In some cases, the positive electrode materialadditionally includes an iron fluoride such as ferric fluoride. Forexample, the metal may be iron and the particles or nanodomains furtherinclude ferric fluoride.

In certain embodiments, some particles or nanodomains contain only themetal and other particles or nanodomains contain only lithium fluoride.In some embodiments, individual particles of the positive electrodematerial include both the metal and lithium fluoride. In one example,the lithium fluoride comprises lithium oxyfluoride.

In certain embodiments, the positive electrode material additionallyincludes (iii) a conductive additive. In some cases, the conductiveadditive is a mixed ion-electron conductor. In some cases, theconductive additive is a lithium ion conductor. In some implementations,the lithium ion conductor is or includes thio-LISICON, garnet, lithiumsulfide, FeS, FeS₂, copper sulfide, titanium sulfide, Li₂S—P₂S₅, lithiumiron sulfide, Li₂S—SiS₂, Li₂S—SiS₂—LiI, Li₂S—SiS₂—Al₂S₃, Li₂S—SiS₂—GeS₂,Li₂S—SiS₂—P₂S₅, Li₂S—P₂S₅, Li₂S—GeS₂—Ga₂S₃, or Li₁₀GeP₂S₁₂.

In some implementations, the median characteristic dimension of theparticles or nanodomains is about 5 nm or less. In some materials, themetal in the particles is present as metal nanodomains having a mediandimension of less than about 20 nm. In some materials, the particles ornanodomains are substantially homogeneous within a volume of about 1000nm³.

Another aspect of the disclosure concerns glassy conversion materialsfor a positive electrode. Such materials may be characterized by ametal, one or more oxidizing species, and a reducing cation mixed at ascale of less than 1 nm. Further, the glassy conversion material issubstantially homogeneous within a volume of 1000 nm³. In someimplementations, the cation comprises lithium, sodium, or magnesium. Insome implementations, the glassy conversion material is substantiallyfree from clumps of a single species the metal or oxidizing species witha volume of greater than 125 nm³.

Another aspect concerns positive electrodes that may be characterized bythe following features: (a) a current collector; and (b)electrochemically active material in electrical communication with thecurrent collector. The electrochemically active material includes (i) ametal component, and (ii) a lithium compound component intermixed withthe metal component on a distance scale of about 20 nm or less. Further,the electrochemically active material, when fully charged to form acompound of the metal component and an anion of the lithium compound,has a reversible specific capacity of about 350 mAh/g or greater whendischarged with lithium ions at a rate of at least about 200 mA/g. Insome cases, the electrochemically active material is provided in a layerhaving a thickness of between about 10 nm and 300 μm.

In some cases, the positive electrode additionally includes aconductivity enhancing agent such as an electron conductor componentand/or an ion conductor component. Some positive electrodes include amixed ion-electron conductor component. In some cases, the mixedion-electron conductor component contains less than about 30 percent byweight of the cathode. Examples of the mixed ion-electron conductorcomponent include thio-LISICON, garnet, lithium sulfide, FeS, FeS₂,copper sulfide, titanium sulfide, Li₂S—P₂S₅, lithium iron sulfide,Li₂S—SiS₂, Li₂S—SiS₂—LiI, Li₂S—SiS₂—Al₂S₃, Li₂S—SiS₂—GeS₂,Li₂S—SiS₂—P₂S₅, Li₂S—P₂S₅, Li₂S—GeS₂—Ga₂S₃, and Li₁₀GeP₂S₁₂. In someembodiments, the mixed ion-electron conductor component has a glassystructure.

In some positive electrodes, the metal component is a transition metal,aluminum, bismuth, or an alloy of any of these. In some cases, the metalcomponent is copper, manganese, cobalt, iron, or an alloy of any ofthese. For example, the metal component may be an alloy of iron withcobalt and/or manganese. In some positive electrodes, the metalcomponent includes grains of metal with a median characteristic lengthof about 5 nm or less.

In certain embodiments, the lithium compound component is selected fromlithium halides, lithium sulfides, lithium sulfur-halides, lithiumoxides, lithium nitrides, lithium phosphides, and lithium selenides. Inone example, the lithium compound component is lithium fluoride. In afurther example, the lithium compound component is lithium fluoride andthe metal component is manganese, cobalt, copper, iron, or an alloy ofany of these. In some positive electrodes, the lithium compoundcomponent contains particles or nanodomains having a mediancharacteristic length scale of about 5 nm or less. In certainembodiments, the lithium compound component includes an anion that formsa metal compound with the metal on charge, and the metal compound andlithium ions undergo a reaction to produce the metal and the lithiumcompound component, and the reaction has a Gibbs free energy of at leastabout 500 kJ/mol.

In some cases, the electrochemically active material, when fullycharged, has a specific capacity of about 300 mAh/g or greater whendischarged with lithium ions at a rate of at least about 6000 mA/g at atemperature of about 100° C. In certain embodiments, the positiveelectrode exhibits an average voltage hysteresis that is less than about1V when cycled between 1V and 4V vs. Li at a temperature of 100° C. andcharged at a rate of about 200 mAh/g of positive electrode activematerial.

Another aspect of the disclosure concerns a solid-state energy storagedevice characterized by the following features: (i) an anode, (ii) asolid-state electrolyte, and (iii) a cathode including (a) a currentcollector, (b) electrochemically active material in electricalcommunication with the current collector. The electrochemically activematerial includes (i) a metal component, and (ii) a lithium compoundcomponent intermixed with the metal component on a distance scale ofabout 20 nm or less. Further, the electrochemically active material hasa reversible specific capacity of about 600 mAh/g or greater whendischarged with lithium ions at a rate of at least about 200 mA/g at 50°C. between 1 and 4V versus a Li.

In some energy storage devices, the anode, solid state electrolyte, andcathode, together provide a stack of about 1 μm to 10 μm thickness. Insome designs, the electrochemically active material is provided in alayer having a thickness of between about 10 nm and 300 μm.

In some energy storage devices, the electrochemically active materialhas a reversible specific capacity of about 700 mAh/g or greater whendischarged with lithium ions at a rate of at least about 200 mA/g. Insome designs, the device has an average voltage hysteresis less thanabout 1V when cycled at a temperature of 100° C. and a charge rate ofabout 200 mAh/g of cathode active material.

In some cases, the cathode additionally includes a conductivityenhancing agent such as an electron conductor component and/or an ionconductor component. Some positive electrodes include a mixedion-electron conductor component.

In certain embodiments, the metal component is a transition metal,aluminum, bismuth or an alloy of any of these. For example, the metalcomponent is iron or an alloy thereof. In another example, the metalcomponent is copper, cobalt, manganese, iron, or an alloy of any ofthese. In some cathodes, the metal component is provided as grains ofmetal with a median characteristic length of about 5 nm or less.

In certain embodiments, the lithium compound component is selected fromthe group of lithium halides, lithium sulfides, lithium oxides, lithiumnitrides, lithium phosphides, lithium selenides, and combinationsthereof. In example, the lithium compound component is lithium fluoride.In a further example, the a lithium compound component is lithiumfluoride and the metal component comprises manganese, cobalt, copper oriron (e.g., iron or an alloy thereof). In certain embodiments, thelithium compound component is provided as particles or nanodomainshaving a median characteristic length scale of about 5 nm or less. Insome energy storage devices, the lithium compound component contains ananion that forms a metal compound with the metal on charge, and when themetal compound and lithium ions undergo a reaction to produce the metaland the lithium compound component, the reaction has a Gibbs free energyof at least about 500 kJ/mol. In some cases, the cathodeelectrochemically active material contains a combination of two or moreof lithium fluoride, iron, lithium metal and iron fluoride.

Another aspect of the disclosure concerns battery cells characterized bythe following features: (a) an electrolyte; (b) a negative electrode;and (c) a solid-state conversion material provided with an interface tothe electrolyte, the solid-state conversion material that in thedischarged state comprises a metal, one or more oxidizing species, and areducing cation mixed at a scale of less than 1 nm. In certainembodiments, the conversion material is substantially glassy. The metalmay be a transition metal material such as cobalt, copper, nickel,manganese and/or iron material. The cation may be lithium, sodium,and/or magnesium material.

In another aspect, the disclosure pertains to battery devicescharacterized by the following features: (a) an anode region containinglithium; (b) an electrolyte region; (c) a cathode region containing athickness of lithium fluoride material configured in an amorphous state;and (d) a plurality of iron metal particulate species spatially disposedwithin an interior region of the thickness of lithium fluoride to form alithiated conversion material. Further, the battery device has an energydensity characterizing the cathode region of greater than about 80% of atheoretical energy density of the cathode region. In certainembodiments, the first plurality of iron metal species is characterizedby a diameter of about 5 nm to 0.2 nm. In certain embodiments, thethickness of lithium fluoride material is characterized by a thicknessof 30 nm to 0.2 nm. In some cases, the thickness of lithium fluoridematerial is homogeneous. In certain embodiments, the cathode region ischaracterized by an iron to fluorine to lithium ratio of about 1:3:3. Incertain embodiments, the cathode region is characterized by an iron tofluorine to lithium ratio from about 1:1.5:1.5 to 1:4.5:4.5.

An aspect of the disclosure pertains to methods of fabricating abattery. In some cases, such methods may be characterized by thefollowing operations: (a) providing a cathode containingelectrochemically active material in electrical communication with thecurrent collector; and (b) combining the cathode with an anode and asolid-state electrolyte to form the battery. The electrochemicallyactive material includes (i) a metal component, and (ii) a lithiumcompound component intermixed with the metal component on a distancescale of about 20 nm or less. Further, the cathode electrochemicallyactive material, when fully charged to form a compound of the metalcomponent and an anion of the lithium compound, has a reversiblespecific capacity of about 350 mAh/g or greater when discharged withlithium ions at a rate of at least about 200 mA/g between e.g., 1V to 4Vversus a lithium standard electrode at 50° C.

In some embodiments, the electrochemically active material is preparedby solid state synthesis. In one example, the solid phase synthesisincludes mixing and milling precursors or reactants for theelectrochemically active material. In one example, the solid phasesynthesis includes reacting an iron containing compound and a fluoride.

In some embodiments, the electrochemically active material is preparedby evaporation of one or more precursors of the electrochemically activematerial. In one example, evaporation involves evaporating a precursorselected from the group consisting of LiF, FeF3, FeF2, LiFeF3, Fe, andLi. In one example, evaporation involves reacting an evaporatedprecursor in an environment containing a gas selected from the groupconsisting of F₂, CF₄, SF₆, and NF₃.

In some embodiments, the electrochemically active material is preparedby (a) melting one or more precursors of the electrochemically activematerial; (b) atomizing the melted precursors into particles; and (c)cooling the particles to mix the metal component and the lithiumcompound component at a length scale of about 20 nm or less.

In some implementations, the cooling takes place at a rate of at leastabout 100 degrees Kelvin per second. In some implementations, thecooling is performed by contacting the particles on a spinning coolingsurface.

Another aspect of the disclosure concerns methods of forming aconversion material, which methods may be characterized by the followingoperations: (i) providing a first precursor material, the firstprecursor material containing a metal material; (ii) providing a secondprecursor material, the second precursor material containing a reducingcation material; (iii) evaporating the first precursor material and thesecond precursor material to vapor state; (iv) mixing the firstprecursor material and the second precursor material in the vapor statewithin a vacuum chamber to form a mixed material within the chamber, themixed material containing the first precursor material and the precursormaterial mixed at a length scale of less than about 20 nm; and (v)collecting the mixed material. In certain embodiments, the firstprecursor material and the second precursor material are characterizedby a tendency of phase separation. In some implementations, theevaporating is performed using a thermal evaporation process, anelectron beam process, or a flash evaporation process. In someimplementations, the methods additionally include an operation ofcooling the mixed material at a rate of at least about 10 degrees Kelvinper second.

Another aspect of the disclosure concerns methods of forming aconversion material, which methods are characterized by the followingoperations: (i) providing a first precursor material containing a metalmaterial; (ii) providing a second precursor material containing areducing cation material; (iii) melting the first precursor material andthe second precursor material to liquid state; (iv) injecting the firstprecursor material and the second precursor into a cooling environment,where the first precursor material and the second precursor materialform a mixed material that is cooled at a rate of at least about 100degrees Kelvin per second to generate formed particles; and (v)collecting the formed particles. In some embodiments, the firstprecursor material and the second precursor material are characterizedby a tendency of phase separation. In some embodiments, the formedparticles contain the first precursor material and the precursormaterial mixed at a length scale of less than about 20 nm.

In some implementations, the cooling environment is a cooling chamber.The cooling environment may include a cooling surface. The coolingsurface may be characterized by a high thermal conductivity. In somecases, the cooling includes exposing the mixed material to lowtemperature gaseous species.

In some implementations, the methods additionally include the followingoperations: injecting the first precursor material into a common regionof the cooling chamber from a first nozzle; and injecting the secondprecursor material into the common region of the cooling chamber from asecond nozzle.

In certain embodiments, the methods additionally include the followingoperations: combining the first precursor material and the secondprecursor material to form a combined material; and injecting thecombined material into the cooling chamber.

The operation of melting of the first precursor material may beperformed separately from melting the second precursor material. Themelting may be performed at different temperatures for the firstprecursor material and the second precursor material.

Another aspect of the disclosure concerns forming a battery cell by: (i)receiving a layer of cathode current collector; (ii) forming a cathoderegion comprising a nanostructured conversion material comprisingnanodomains of iron and nanodomains of lithium fluoride to form; (iii)forming a solid electrolyte layer overlaying the cathode region; and(iv) forming an anode and/or anode current collector overlaying thesolid electrolyte layer. The nanostructured conversion material may beatomically mixed. In certain embodiments, the method includes theadditional operation of forming electrical contacts to the cathodecurrent collector and the anode and/or anode current collector.

These and other features of the disclosed embodiments will be set forthin more detail below with reference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A presents a solid-state energy storage device including an anodeand a cathode spaced apart and separated by a solid-state electrolyte.

FIG. 1B presents a solid-state energy storage device with an anodecurrent collector proximate to a anode and a cathode current collectorproximate to a cathode.

FIG. 2A presents a five examples of conversion materials having variousnanodomain and particle formats.

FIG. 2B presents additional examples of particle and nanodomainstructures that may be employed in ferric fluoride and relatedconversion materials.

FIG. 3 schematically depicts a matrix material provided as a continuouslayer that embeds separate particles or nanodomains of active materialand conductivity enhancing agent.

FIGS. 4A-D are simplified diagrams illustrating a process for forming abattery cell according to an embodiment.

FIG. 5 presents an example of a small multi-stack battery configuration.

FIG. 6 presents a plot of cell performance measured by cathodevolumetric energy density versus LiF in a laminate structure.

FIG. 7 presents a plot of constant current charge and discharge of a 66nm cathode of 3LiF+Fe at 120° C.

FIG. 8 presents a plot of constant current charge and discharge of a 129nm cathode of 3LiF+Fe at 120° C.

FIG. 9 presents a plot of a constant current discharge of a cell whosecathode is 134 nm (3LiF+Fe+S_(0.14)).

FIG. 10 presents a plot of a constant current discharge of a cell whosecathode is 134 nm (3LiF+Fe+S_(0.53)).

FIG. 11 provides a plot of cell performance measured by cathodevolumetric energy density versus the LiF material length scale in alaminate structure.

FIG. 12 is a plot of cell performance measured by cathode volumetricenergy density versus Fe length scale in a laminate structure.

FIG. 13 provides a cross-section view of nanostructured conversionmaterial on a scale of about 5 nm.

FIG. 14 provides a cross-section view of nanostructured conversionmaterial on a scale of about 2 nm.

FIG. 15 provides a cross-section view of nanostructured conversionmaterial on a scale of about 2 nm.

FIG. 16 is a plot illustrating an example of the benefits ofnanostructuring a conversion material and maintaining uniformity ofcomposition.

FIG. 17 presents theoretical energy density of lithiated conversioncathode materials versus a standard Li anode.

FIG. 18 presents theoretical specific energy of lithiated conversioncathode materials versus the standard Li anode.

FIG. 19 presents a plot (voltage (measured against a standard lithiumelectrode) versus cathode material active capacity) for the first 5cycles of charge/discharge of a cupric fluoride sample.

FIG. 20 presents discharge energy for samples containing certaintransition metal alloys used in a conversion material.

FIG. 21, capacity and hysteresis statistics are provided for thefollowing conversion material samples: FeCo+LiF, FeMn+LiF, Fe₃Co+LiF,and a control sample of Fe+LiF.

DETAILED DESCRIPTION

Introduction

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

In the following detailed description, numerous specific details are setforth in order to provide a more thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without necessarily being limitedto these specific details. In other instances, well-known structures anddevices are shown in block diagram form, rather than in detail, in orderto avoid obscuring the present invention.

All the features disclosed in this specification, (including anyaccompanying claims, abstract, and drawings) may be replaced byalternative features serving the same, equivalent or similar purpose,unless expressly stated otherwise. Thus, unless expressly statedotherwise, each feature disclosed is one example only of a genericseries of equivalent or similar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph f. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph f.

Please note, if used, the labels left, right, front, back, top, bottom,forward, reverse, clockwise and counter clockwise have been used forconvenience purposes only and are not intended to imply any particularfixed direction. Instead, they are used to reflect relative locationsand/or directions between various portions of an object.

The disclosed embodiments concern positive electrodes containing a highcapacity material that reversibly undergoes a redox reaction at a highrate over many cycles of charge and discharge. Such materials aresometimes referred to herein as “conversion” materials.

In general, intercalation and/or conversion materials can be used inbattery systems. For example, a positive electrode material may be usedfor intercalation or conversion with lithium. Intercalation materials,which can be prepared at a macro scale or at a nano scale, are commonlyused in and typically have relatively low energy density (e.g., lessthan about 800 Wh/kg of active material). Conversion materials, incontrast, can provide much higher energy density (e.g., about 1000-2500Wh/kg of active material). Battery systems and structures utilizingconversion material are described in U.S. Provisional Patent ApplicationNo. 61/778,455, filed 13 Mar. 2013, titled “IRON, FLUORINE, SULFURCOMPOUNDS FOR BATTERY CELL POSITIVE ELECTRODES”, and U.S. ProvisionalPatent Application No. 61/674,961, filed Jul. 24, 2012, and titled“NANOSCALE LITHIUM COMPOUND AND METAL ELECTRODES”, both of which areincorporated by reference herein in their entireties.

In certain embodiments, the conversion material includes an oxidizingspecies, a reducing cation species, and a metal species. These speciesare sometimes referred to herein as constituents or components. Theoxidizing species is typically a strongly electronegative element,compound, or anion. Examples of oxidizing species anions include halides(fluorides, chlorides, bromides, and iodides), oxides, sulfides, and thelike. The reducing cation species is typically an electropositiveelement or cation such as lithium, sodium, potassium, or magnesium andions thereof. The metal species is typically less electropositive thanthe reducing cation species. Transition metals are sometimes used as themetal species. Examples include cobalt, copper, nickel, manganese, andiron. The conversion material may contain two or more oxidizing species,two or more reducing cation species, and/or two or more metal species.

As is understood in the art, batteries and their electrodes undergoelectrochemical transitions during discharge and—in the case ofsecondary or rechargeable batteries—charge. The charge and dischargestates of certain conversion materials will now be described.

Discharged state—In the discharged state, the metal species aregenerally more reduced than in the charged state. For example, the metalspecies is an elemental state or a lower oxidation state or positivevalence (e.g., +2 rather than +3). Further, during discharge, theoxidizing species will pair with the reducing cation species and unpairfrom the metal species. Still further, during discharge, the reducingcation species tends to move into the positive electrode where itbecomes oxidized by pairing with the oxidizing species. Pairing istypically manifest by formation of a chemical bond such as a covalent orionic bond.

Depending on the implementation, in the discharged state, the conversionmaterial may include an elemental metal material, one or more oxidizingspecies, and a reducing cation material. As an example, the dischargestate may include at least an elemental metal such iron and a reducingcation halide such as lithium fluoride. The constituents of thedischarged conversion material may be intimately distributed with oneother in the discharged material. As described more fully below, thesematerials may be intermixed or distributed at a scale of about 20 nm orsmaller.

It should be understood that a positive electrode of the type describedherein may exist in various states of charge. In some cases, a batteryis designed or operated so that full discharge is never attained. Thus,if the fully charged conversion material is ferric fluoride for example,the “fully” discharged positive electrode may contain a mixture ofelemental iron, lithium fluoride, and some ferric fluoride, and possiblysome ferrous fluoride. The use of “discharged” or “discharged state”herein is a relative term, referring only to a state of a conversionmaterial that is more discharged than a charged state of the material.By the same token, the use of “charged” or “charged state” herein refersto a state of the conversion material that is more charged than acorresponding discharge state for the material.

Charged state—In a charged state, the metal species tends to pair withthe oxidizing species often forming a compound. During charging, theoxidizing species tends to unpair from the reducing cation species andpair with the metal species. The reducing cation species tend to moveout of the positive electrode and migrate and/or diffuse to the negativeelectrode where they exist in a more strongly reduced state (e.g., as anelement metal such as lithium metal or lithium inserted in a matrix suchas carbon or silicon).

As an example, during charge, elemental iron may pair with fluorideanions to form ferric fluoride and/or ferrous fluoride. Concurrently,fluoride anions may unpair from a reducing cation fluoride such aslithium fluoride. The now freed lithium cation migrates and/or diffusesto the positive electrode where it is reduced to elemental lithium or alithium intercalation material.

The scale of the constituents in the conversion material, whether in thecharged or discharged state, influences relevant electrochemicalproperties of the materials. It has been found that conversion materialshaving their constituents or components separated by very smalldistances, sometimes on the order of atomic scale, may possess certainperformance benefits as compared to conversion materials that haveconstituents separated by greater distances. In some embodiments, theconstituents are separated by distance no greater than about 20 nm. Suchconversion materials have been observed to provide various benefits suchas increased cycle lifetime, improved efficiency, improved energydensity, improved power density, and improved low temperatureperformance. The term “nanostructured” is sometimes used to refer toconversion materials in charged or discharged states in which theconstituent materials are separated from one another at a scale of about20 nm or less

In some embodiments, in the discharged state, the conversion materialcontains discrete domains of an elemental metal (or an alloy thereof)and a lithium compound. In some embodiments, the discrete grains ofmetal or alloy are embedded in a continuous matrix of the lithiumcompound. In other embodiments, the metal or alloy and lithium compoundare present in small particles or other discrete structures. In eithercase, the various components of the conversion materials may be mixedand/or otherwise exist at a nanostructured scale. The individual domainsmay be nanodomains. Nanodomains may have an average or mediancharacteristic dimension of about 20 nm or less or about 10 nm or lessor about 5 nm or less. Using ferric fluoride as an example conversionmaterial, the nanodomains may be primarily iron and lithium fluoride inthe discharged state. In the charged state, the nanodomains areprimarily ferric fluoride. In both charge states, the nanodomains may becrystalline or amorphous/glassy. Domains may be compositionallyhomogenous (e.g., containing exclusively metal species) or inhomogeneous(e.g., composed of a combination of metal species, oxidizing species,and reducing cation species).

In various embodiments, the conversion material is formed or mixed suchthat its constituents are separated on a scale of about 1 nm or less.Some such materials may be characterized as glassy or amorphous. Aglassy material may be viewed as one that is substantiallynon-crystalline, substantially uniform in composition, and substantiallylacking in long-range order. In some examples, a glassy conversionmaterial is substantially homogeneous (compositionally and/ormorphologically) within a volume of 1000 nm³.

The conversion material is structured at a nano level (e.g., less than20 nm in length). In one example, FeF₃ molecules in a charged conversionmaterial may be characterized by a glassy or amorphous structure andbeing substantially homogeneous. In some examples, in the dischargedstate, the conversion material may include a glassy compound of lithium,sodium and/or magnesium. Such glassy or amorphous structures may beprovided as particles, layers, etc. Within these particles or layers,the constituent metal, oxidizing, and reducing cation species are, onaverage, separated from one another by no greater distance than thelength scales noted. In some cases, particles having a glassy oramorphous state substantially unagglomerated. In other cases, at leastsome of the particles form agglomerates.

Depending on the implementation, in the discharged state, the conversionmaterial may include a metal material, one or more oxidizing species,and a reducing cation material separated at a scale of less than about20 nm. More specifically, the conversion materials are substantiallyhomogeneous within a volume of about 1000 nm³ or less. In an example,molecules including metal, oxidizing species, and a reducing cation arestructured at a nanometer scale. As presented in an example above, thedischarged material may include an elemental form of the metal speciesand a compound of the reducing metal cation and an anion of theoxidizing species.

In the charged state, the conversion material contains a compound of themetal. In some embodiments, the electrochemical charge-dischargereaction at the positive electrode may be represented, withoutstoichiometry considerations, by the following equation:M+LiX

MX+Li⁺+e⁻where M is the metal species and X is the oxidizing species; e.g., ananion or electron rich species of an element such as a halide, oxygen,sulfur, phosphorus, nitrogen, selenium, or combination of such elements.In a specific example, the oxidizing species is combination of a halogenion and a chalcogen ion (e.g., fluoride and sulfide). In certainvariations of the above-referenced chemical equation, lithium isreplaced with sodium, potassium, magnesium, or other electropositivemetal ion.

The metal compound MX present in the charged positive electrode materialshould react with lithium ions according to discharge path of the aboveequation. Typically, the discharge reaction is associated with anappropriately large Gibbs free energy when considering the full cellreaction Li+MX→LiX+M. The Gibbs energy will correspond to the cellvoltage of the reaction by ΔG_(rxn)=−E*n*F where E is the voltage, n isthe number of electrons that react and F is the Faraday constant. Incertain embodiments the Gibbs energy of the reaction is at least about500 kJ/mol or at least about 750 kJ/mol or at least about 1 MJ/mol.

In certain implementations, the voltage of a fully charged positiveelectrode is at least about 2.0 V versus a lithium metal electrode or atleast about 3.0 V versus a lithium metal electrode or at least about 4.0V versus a lithium metal electrode or at least about 4.5 V versuslithium metal electrode.

In the charged state, the positive electrode conversion material maymaintain the general morphological characteristics present in thedischarged state. These characteristics include constituent separationdistance (e.g., particle or crystallite size), matrix structure (e.g.,glassy), etc. In some cases, the material will expand in the dischargedstate. Depending on the material, the volume change may be about 5% orgreater or about 10% or greater.

Examples of suitable metal species M include transition metals, aluminumand bismuth. In some cases, the metal is selected from first rowtransition metals. Specific examples transition metals that may be usedinclude vanadium, chromium, copper, iron, cobalt, manganese, nickel,ruthenium, titanium, silver, and tungsten. Alloys of such metals mayalso be used. Examples of such alloys include iron alloyed with cobaltand iron alloyed with manganese. Examples of suitable oxidizing speciesanions X include O, S, N, P, F, Se, Cl, I, and combinations thereof.

Examples of suitable charged state positive electrode materials includesulfides, oxides, halides, phosphides, nitrides, chalcogenides,oxysulfides, oxyfluorides, sulfur-fluorides, and sulfur-oxyfluorides. Invarious embodiments, the charged conversion material includes one ormore of the following: AgF; AlF₃; BiF₃; B₂O₃; Co₃O₄; CoO; CoS₂;Co_(0.92)S; Co₃S₄; Co₉S₈; CON; Co₃N; CoP₃; CoF₂; CoF₃; Cr₂O₃; Cr₃O₄;CrS; CrN; CrF₃; CuO; Cu₂O; CuS; Cu₂S; CuP₂; Cu₃P; CuF₂; Fe₂O₃; FeO;FeOF; FeS₂; FeS; Fe₂S₂F₃; Fe₃N; FeP; FeF₂, FeF₃; FeOF; Ga₂O₃; GeO₂,MnO₂; Mn₂O₃; Mn₂O₅; MnO; MnS; MnS₂; MnP₄; MnF₂, MnF₃, MnF₄, MoO₃; MoO₂;MoS₂; Nb₂O₅; NiO; NiS₂; NiS; Ni₃S₂; Ni₃N; NiP₃; NiP₂; Ni₃P; NiF₂; PbO;RuO₂; Sb₂O₃; SnF₂; SnO₂; SrO₂; TiS₂; TiF₃; V₂O₃; V₂O₅; VF₃; WS₂; ZnF₂;and combinations thereof.

The conversion material may be discharged with a cation that undergoesan exothermic reaction with the conversion material. The cation is oftenlow-cost and lightweight (relative small atomic mass). Certain examplesinclude Mg, Na, and Li. As an example for FeF₃ conversion material andLi cation, the conversion material when created, or when in thedischarged state, may be an amorphous mixture of lithium, iron, andfluorine in the ratio of approximately Li₃FeF₃. In certain embodiments,the three elements are intimately intermixed on an atomic scale. Invarious implementations, the conversion material is characterized by aniron to fluorine to lithium ratio of from about 1:1.5:1.5 to 1:4.5:4.5.

Certain disclosed embodiments concern use of a redox reaction of lithiumions with a metal fluoride as a source of energy in positive electrodematerials. As an example, a suitable positive electrode material is, inthe charged state, ferric fluoride in very small particles, which may bethe size of quantum dot (e.g., about 5 nm in the smallest cross-section)or in a glassy or amorphous state. In some embodiments, electrodes madeof metal fluoride redox materials are employed in batteries having solidelectrolytes such as inorganic electrolytes. A specific example of suchelectrolyte is LiPON.

In some implementations, the discharge of the positive electrode isaccompanied by the reaction of ferric fluoride or other transition metalfluoride with lithium ions that have migrated into or inserted into theferric fluoride matrix and there react to form lithium fluoride andelemental iron. The large Gibbs free energy associated with thisreaction provides a very high available energy for a battery. Thisenergy may be compared with that of a standard lithium insertion (orlithium intercalation depending on the electrode matrix) cathodematerials such as lithium cobalt oxide, lithium manganese oxide, lithiumtitanate, and the like used in conventional lithium ion batteries. Thematerials disclosed herein combine during discharge with a large numberof lithium atoms per transition metal. During charge, intercalationreactions involve at most one lithium atom per transition metal (e.g.,as lithium is reduced from Li⁺ to Li⁰, cobalt oxidizes from Co³⁺ toCo⁴⁺), whereas in conversion reactions such as those producing FeF₃, 3lithium atoms react per transition metal. In fact, most insertioncompounds react half a lithium atom per transition metal because theelectrode structure becomes unstable if more than ½ of the lithium isextracted. This is why the transition metal electrode materialsdisclosed herein provide a significantly higher capacity (e.g., about700 mAh/g or greater) than conventional electrode materials, e.g., 140mAh/g for LiCoO₂. This capacity is available even at high rates and overmany cycles when the electrode possesses suitably high ionic andelectronic conductivity as disclosed herein.

A non-oxide cathode also presents safety advantages. A typical Li-ionbattery uses a high voltage oxide cathode that is in thermodynamicdisequilibrium with oxygen gas in the atmosphere. A relation existsbetween the voltage and the thermodynamic oxygen partial pressure; forinstance, at 4.2V vs. Li/Li⁺, the equilibrium oxygen partial pressure ofan oxide, for example LiCoO₂at room temperature is 10⁸⁷ atm (Godshall etal, J ElectrochemSoc, 131 (1984) 543). Kinetics may prevent the rapidevolution of oxygen, but this large driving force will inevitablyinvolve the release of oxygen, this is why batteries must have vents forsafety purposes. If a safety event occurs that raises the temperature ofthe battery or otherwise presents an occasion for oxygen evolution, therapid release of oxygen into the gas phase and the attendant expansionof oxygen as it transitions from solid to gas may result in anexplosion. In contrast, due to the higher stability of lithium halidesrelative to lithium oxide, and the lower voltage of lithium halideelectrodes, the safety risks are substantially lower. At 4V vs. Li/Li⁺and even 100° C., the equilibrium partial pressure of fluorine is 10⁻⁵⁵atm.

A challenge associated with this technology is potentially slow masstransfer of lithium ions through iron fluoride or a lithium fluoridematrix (which may be in the form of particles). As a consequence, thefull capacity of the material is not realized because many reactivesites are inaccessible in a period of time required for charging ordischarging the battery in many applications. Further, the rateperformance of the material is relatively poor given that the diffusionand migration time of lithium ions through the matrix takes too long.Still further, a significant mass transport overpotential is associatedwith charging and discharging these materials. This overpotentialresults in lower energy delivered to the application, more heatgeneration, which can cause problems at a systems level, and lowerefficiency, which increases the cost to the consumer. This challenge mayalso exist in batteries employing conversion materials with metalspecies other than iron, oxidizing species other than fluoride, and/orreducing cation species other than lithium ions, as identified above.

To address the challenge of slow mass transport, the positive electrodematerial that contains elemental metal or alloy and a lithium compound(in the discharged state) or a metal compound (in the charged state) maybe provided in the form of extremely small particles or nanodomains. Incertain embodiments, these particles or domains have a mediancharacteristic dimension of about 20 nm or less or about 10 nm or less.In some aspects, the particles or domains have a median characteristicdimension of about 5 nm or less. In some cases, the conversion materialmay be a glassy or amorphous material. In some implementations, theparticles or domains of the positive electrode have a very tightdistribution, e.g., a standard deviation of about 50% or less. In someimplementations, at least about 90% of the particles or domains in theelectrode have a characteristic dimension of between about 1 and 5 nm.In some embodiments, the particles' characteristic dimension has a d₅₀value of about 20 nm or less or about 10 nm or less or about 5 nm orless. d₅₀ is defined as the characteristic dimension at which 50% of theparticles are smaller. The particles or domains may be present in thesesizes at any point in the life of the positive electrode. In someexamples, the particles or domains are present in these sizes in thepositive electrode as fabricated. In some examples, the particles ordomains are present in these sizes after the first discharge of thepositive electrode, or after the first full charge/discharge cycle ofthe positive electrode. In certain embodiments, the average size of theparticles or domains of the positive electrode do not vary incharacteristic dimension by more than about 500% or by about 100% overmultiple cycles (e.g., 10 cycles, 50 cycles, 100 cycles, or 500 cycles).

The extremely small constituent separation distances described hereprovide a relatively short diffusion path for the lithium or otherelectropositive ions to move from the outside of the particle or domainto the reactive metal compound sites within the particle/domain(discharge) or from a lithium compound within the particle/domain to theparticle/domain surface (charge). During charge, lithium ions must leavelithium fluoride, for example, and transport to the exterior of theparticle/domain where they contact the electrolyte. After leaving aparticle/domain, a lithium ion may have to contact some other ionconductive matrix in the electrode before reaching the electrolyte.Conversely, on discharge lithium ions undergo a journey from theelectrolyte into the body of the electrode where they must travel somedistance before reaching a destination particle/domain, which they enterand pass into before finding a reactive metal compound site. Only afterthis multistage transport does the lithium ion participate in the redoxreaction to generate electrochemical energy (discharge). The reversepath is traversed during charge. The use small separation distances ofactive material permits the positive electrode to operate with improvedrate performance, not available previously.

A further benefit derived from the extremely small constituentseparation distances is the comparatively shorter diffusion distancebetween the metal atom and the anion. As the metal and anion atoms arelarger and more massive, their transport is generally slower than thatof lithium. The provided nanostructure puts metal atoms in closeproximity to anions, reducing the distance they must diffuse.

An additional challenge to realizing the potential benefits ofconversion materials arises from the high surface area/mass ratio ofvery small particles. The large surface area (as a function of mass ofreactive material) results in a relatively large fraction of the activematerial converting to a solid electrolyte interface (SEI) layer, whichextracts much of the available lithium and presents it in an unusableform. It also therefore results in a relatively short cycle life as theSEI layer may continue to grow for a few cycles. The SEI that formsaround a particle which undergoes significant volume changes duringcycling may sometimes crack, providing a fresh surface that must becovered by SEI. The growing SEI contains mass that does not contributeto the energy stored in the battery, and may present a barrier tolithium transport, reducing the rate performance of the battery.

In certain embodiments, this second challenge is addressed by using asolid electrolyte. The solid electrolyte provides an ionicallyconductive medium without consuming significant amounts of activematerial in the formation of SEI layers. Therefore the positiveelectrode material can maintain its intrinsically high reversiblecapacity. It should be understood, however, that in other embodiments,the positive electrodes described herein are used with liquid and gelphase electrolytes.

A typical Li-ion battery uses a flammable hydrocarbon electrolyte (e.g.,a cyclic organic carbonate or mixture of these). If a safety event thatgenerates heat (such as a short circuit) occurs, this electrolyte mayburn, releasing its energy in a fire. If the increased temperatureresults in oxygen evolution from the oxide cathode, an explosion mayresult from the rapid expansion into the gas phase. In contrast, a solidelectrolyte it much more stable—it does not provide a fuel in the eventof a short circuit.

Many types of solid electrolyte layer can be used. In some cases, theelectrolyte material has a relatively high lithium ion conductivity,e.g., at least about 10⁻⁶ Siemens/centimeter or at least about 10⁻³Siemens/centimeter. Examples of inorganic materials that could be usedas the sole electrolyte layer include LiPON and similar lithium ionconductors.

FIG. 1A shows one version of a solid-state energy storage devicedescribed herein. The device (100) includes an anode (140) and cathode(150) spaced apart and a solid-state electrolyte (130) disposed betweenthe anode and cathode.

FIG. 1B shows a version of a solid-state energy storage device with ananode current collector (110) proximate to the anode and a cathodecurrent collector (120) proximate to the cathode. Generally, the currentcollector is a solid conductive substrate in intimate contact with theelectrochemically active material of electrode. Forms of currentcollectors include sheets, foils, foams, meshes, perforated sheets, etc.The current collector should be made from a conductive material that iselectrochemically compatible with the positive electrode material.Examples include copper, aluminum, nickel, tungsten, titanium, tantalum,molybdenum, tantalum nitride, and titanium nitride, steel, stainlesssteel, and alloys or mixtures thereof.

As used herein, a solid-state energy storage device means an energystorage device that includes a solid state anode, a solid state cathode,a solid state electrolyte and other optional components, but does notinclude any non-solid components that function as an anode, a cathode oran electrolyte.

Electrode Capacity

In certain embodiments, the positive electrode conversion material, asfabricated, has a specific capacity of least about 600 mAhr/g of thefully charged positive electrode material. In some embodiments, thepositive electrode material maintains this fully charged capacity overmultiple cycles. The fully charged material is the stoichiometric metalcompound, MX. Examples of such compounds include the sulfides,fluorides, phosphides, selenides, nitrides, oxides, chalcogenides,oxysulfides, oxyfluorides, sulfur-fluorides, sulfur-oxyfluorides andchlorides identified above.

In certain embodiments, the positive electrode conversion material isable to maintain this high capacity at high discharge rates overmultiple cycles. For example, the positive electrode material maymaintain a capacity of at least about 600 mAh/g when discharged at arate of at least about 200 mA/g of fully charged positive electrodematerial. In some implementations, the material maintains this capacityat higher discharge rates of at least about 600 mA/g of fully chargedpositive electrode material. In certain embodiments, the materialmaintains the capacity at discharge rates of up to about 6,000 mA/g offully charged positive electrode material. This discharge rate may bemaintained as a constant value or may vary over discharge withoutdropping below 200 mA/g. In some embodiments, the positive electrodematerial maintains a high capacity at high rates (e.g., 600 mAh/g at 200mA/g) after a subsequent charge. In some cases, the electrode materialis able to maintain such high rate capacity over about 10 cycles ormore. Often it will be able maintain this high rate capacity evenlonger, e.g., over about 20 cycles or more, or over about 50 cycles ormore, or over about 100 cycles or more, or over about 500 cycles ormore. In each cycle the positive electrode material discharges the full600 mAh/g charge. Such cycling may be conducted such that the voltage ofthe positive electrode is between 4V and 1V vs. Li/Li⁺. In someembodiments, the charge rate may be higher than 200 mA/g, higher than600 mA/g, or higher than 6,000 mA/g and the material maintains acapacity of about at least 600 mAh/g.

High capacity performance may be achieved when cycling over a range oftemperatures, e.g., from about 0 degrees Celsius to 100 degrees Celsiusor about 20 degrees Celsius to 100 degrees Celsius.

In one version, the conversion material provides a capacity of greaterthan about 350 mAh/g of active material when cycled between 1 and 4 Vversus a lithium metal negative electrode at about 100 degrees Celsiuswith a charge/discharge rate of 200 mA/g. In other versions, theelectrode material provides a capacity of greater than about 500 mAh/g,or greater than about 600 mAh/g or greater than about 700 mAh/g, in eachcase the capacity value is for the active material cycled in the voltagerange of 1 to 4 V versus a lithium metal negative electrode when cycledat about 100 degrees Celsius with a charge/discharge rate of 200 mA/g.In another version, the electrode materials described herein provide acapacity of between about 350 and 750 mAh/g when cycled between 1 and 4V against a lithium metal negative electrode at about 100 degreesCelsius with a charge/discharge rate of 200 mA/g. In another version,the electrode materials may have a specific capacity of greater thanabout 400 mAh/g when discharged between 1 and 4.5V versus a standardlithium metal electrode (Li/Li⁺) at a rate of 400 mA/g and a temperatureof 120° C. or between 1.5 to 4V vs. Li at a rate greater than 1 C and atemperature above 50° C.

In some cases, positive electrodes fabricated from such materials have ahigh average discharge voltage greater than about 2V when dischargedunder above conditions. The high performance positive electrodematerials disclosed herein maintain their good performance (e.g., highspecific capacity, high energy density, high average discharge voltage,and low hysteresis) even when discharged at high rates. As shown in theexamples below, their performance may not significantly degrade when therate of discharge increases from 10 C to 100 C.

In another version, devices employing the positive electrode materialsdescribed herein provide an average voltage hysteresis of less than 1Vin the voltage range of 1 to 4 V versus a lithium metal electrode atabout 100 degrees Celsius with a charge/discharge rate of 200 mA/g. Inanother version such devices provide an average voltage hysteresis ofless than 0.7 V when cycled between 1 and 4 V versus a lithium metalelectrode at about 100 degrees Celsius with a charge/discharge rate of200 mA/g. In an embodiment, the devices provide an average voltagehysteresis of less than about 1V when cycled between 1 and 4V versus alithium metal electrode at about 100 degrees Celsius with acharge/discharge rate of 600 mA/g. In an embodiment, the devices providean average voltage hysteresis of less than about 1V when cycled between1.5 and 4V versus a lithium metal electrode at about 50 degrees Celsiuswith a charge/discharge rate of 200 mA/g. This hysteresis level ismaintained for at least 10 cycles or at least 30 cycles or at least 50cycles or at least 100 cycles.

Voltage hysteresis is the difference between the discharge voltage andthe charge voltage, both varied as a function of state of charge. Itrepresents the inefficiency of the battery—energy lost to heat, oftendue to sluggishness of either ion transport or reactions. As a resultthe overvoltages are required to drive the reactions, which cause thedischarge voltage to be lower than the open circuit voltage and thecharge voltage to be higher than the open circuit voltage. Lowhysteresis means that the battery is efficient.

In the following discussion various positive electrode compositions arepresented. In each of these, the particle/domain shapes and sizes may bevaried as discussed. As examples, the particles/domains of activematerial in the positive electrode have a median characteristicdimension of about 20 nm or less, or about 10 nm or less, or about 5 nmor less. In some implementations, the material is glassy or amorphous.In some embodiments, particles/domains of the material have a standarddeviation of about 50% or less. In some embodiments, the characteristicdimension of the particles/domains has a d₅₀ value of about 20 nm orless, or about 10 nm or less, or about 5 nm or less.

Cathode Active Component—Metal Component and a Lithium CompoundComponent

In one version of the devices described previously, when the device isin the discharged state the cathode includes an active component(conversion material) that includes an elemental form of a metal oralloy component and a lithium compound component.

Generally the metal component can be any metal or mixture or alloy ofmetals. In one version the metal component is a transition metal ormixture or alloy of transition metals. In one version the metalcomponent is selected from Bi, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Wand Ru, or mixtures or alloys of the forgoing. In one version the metalcomponent is selected from Fe, Cu, Mn and Co. In one version the metalcomponent is Fe. In one version the metal component is Cu. In oneversion the metal component is Co. In one version, the metal componentis an alloy of iron with another metal such as Co or Mn.

In one version, the metal component includes a mixture or alloy of afirst metal and a second metal. In one version of mixed metal component,the metal component includes separate nanodomains of the first metal andthe second metal. In another version, the metal component includesnanodomains of a mixture or alloy of the first and second metals. In oneversion, the first metal is Fe and the second metal is Cu. Generally thelithium compound component is any lithium compound that upon charging ofthe device yields (i) lithium ions, which migrate to the anode, and (ii)an anion that reacts with the metal component to provide a metalcompound component. In the charged state, therefore, the cathodematerial comprises a metal compound component. The anion in the lithiumcompound may generally be any anion that forms the lithium compound inthe discharged state and the metal compound in the charged state. In oneversion the lithium compound is a lithium halide, lithium oxide, lithiumsulphide, lithium nitride, lithium phosphide, lithium sulfur-halide,lithium hydride, or mixtures thereof. In one version the lithiumcompound is a lithium halide. In one version the lithium compound islithium fluoride.

In one version, the “conversion reaction,” may be written as:aM+bLi_(c)X

M _(a)X_(b)+(b*c)Li⁺+(b*c)e ⁻

M _(a)X_(b)+(b*c)Li  (1)

The left hand side of equation 1 represents the cathode active materialsin the discharged state, where the cathode active component comprises ametal component, M, and a lithium compound component, Li_(n)X. c is theformal oxidation state of the anion X.

The right hand side of equation 1 represents the system in the chargedstate in which the cathode active materials have been converted into themetal compound component, M_(a)X_(b), and the Li ions are provided fordiffusion through the electrolyte to the anode and the electrons areprovided to the external circuit.

X is generally any anionic species forming stable compounds, Li_(n)X andM_(a)X_(b), with lithium and metal, M, respectively. M can generally beany metal. In one version, M is a transition metal. In one version, M isselected from Bi, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, W and Ru. In oneversion, M is selected from Fe, Co and Cu. In one version M is Cu. Inone version M is Fe. In one version M is Co.

Specific examples of metal compounds, M_(a)X_(b), that may be usedinclude, without limitation, the following:

X = O X = S X = N X = P X = F Bi BiF₃ Ti TiF₃ V VF₃ Cr Cr₂O₃ CrS CrNCrF₃ Mn MnO₂, MnS MnP₄ Mn₂O₅, MnO Fe Fe₂O₃, FeO FeS₂, FeS Fe₃N FeP FeF₃,FeF₂ Co Co₃O₄, CoO CoS₂, CoN, Co₃N CoP₃ CoF₂, CoF₃ Co_(0.92)S, Co₉S₈ NiNiO NiS₂, NiS, Ni₃N NiP₃, NiP₂, NiF₂ Ni₃S₂ Ni₃P Cu CuO, Cu₂O CuS, Cu₂SCuP₂, Cu₃P CuF₂ Mo MoO₃, MoS₂ MoO₂ W WS₂ Ru RuO₂

In some implementations, the material described here is provided inparticulate form (containing a collection of discrete unconnectedparticles). In some embodiments, it is provided in the form of one ormore continuous layers having a matrix such as the lithium compound oran ion conductor with embedded nanodomains or regions of the metalcomponent and/or the lithium compound component. In some embodiments,individual particles contain mixtures of the metal component and thelithium compound component. In some embodiments, some particles containsolely the metal component. In some embodiments, some particles containsolely the lithium compound component.

FIG. 2A presents a four examples of electrode formats. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. It is to be understood thatthe particles or domains described above are nano-structured (e.g.,separated from one another by less than about 20 nm length scale), andthese particles or domains may be combined to form primary and secondaryparticle structures shown in Examples 1-4.

Example 1 (top left of FIG. 2A) depicts an embodiment in which theelectrode active material includes non-encapsulated nanodomains oflithium fluoride, elemental metal, and metal fluoride. Such material mayexist at any state of charge, but will most typically exist at or nearfull discharge. Example 2 (top right) depicts an electrode format inwhich metal fluoride nanoparticles and lithium fluoride nanoparticlesare encapsulated in an elemental matrix. In each of the encapsulationexamples, the encapsulation unit may exist as distinct particles or as acontinuous layer. Example 3 (bottom left) illustrates a format in whicha metal fluoride matrix encapsulates lithium fluoride nanodomains andelemental metal nanodomains. Example 4 (bottom right) depicts a formatin which lithium fluoride encapsulates metal fluoride particles ornanodomains and elemental metal particles or nanodomains.

FIG. 2B presents additional examples of particle and nanodomainstructures that may be employed in ferric fluoride and relatedconversion materials. In the example of FIG. 2B, the structure at theupper left side is a primary particle 211 that may be found in adischarged cathode. The primary particle 211 includes discretenanodomains of iron metal 213 and lithium fluoride 215. Often, a primaryparticle has a characteristic cross-sectional dimension of about 100 nmor less. As mentioned, the nanodomains that make up a primary particlehave cross-sectional dimensions of about 20 nm or less (e.g., about 5 nmor less). In some cases, the nanodomains are compositionallyhomogeneous.

The top right structure in FIG. 2B represents a secondary particle 217(not drawn to scale) of discharged ferric fluoride conversion material.Secondary particles are made up of primary particles 211, such as thosepresented in the top left structure, and possibly particles of anionically conductive material and/or electronically conductive material219. Secondary particles may be agglomerates or clumps of primaryparticles and optionally particles of ionically/electronicallyconductive materials. In some implementations, secondary particles arepresent in a slurry used to coat a positive current collector whenforming the cathode. In certain embodiments, secondary particles have across-sectional dimension of about 0.1 to 5 micrometers. All dimensionspresented in the discussion of FIG. 2B are median values.

The lower left and lower right structures presented in FIG. 2B representa primary particle 221 and a secondary particle 223, respectively, offully charged ferric fluoride conversion material. Other conversionmaterials may be substituted for ferric fluoride and its dischargeproducts in the structures presented in FIG. 2B.

The relative amounts of the lithium compound component and the metalcomponent can vary widely, but should be appropriate for a battery cell.In other words, the components should be provided in relative amountsthat do not introduce substantial unused material that will notcontribute to electrochemical energy conversion or enhance conductivity.In some embodiments employing iron as the metal component, the moleratio of iron to lithium in the positive electrode active material isabout 2 to 8, or about 3 to 8. In some embodiments employing valence 2metals such as copper, the mole ratio of metal to lithium in thepositive electrode active material is about 1 to 5. In variousimplementations, the positive electrode material is characterized by aniron to fluorine to lithium ratio of about 1:3:3 or from about 1:1.5:1.5to 1:4.5:4.5.

It is to be appreciated that while FIGS. 2A and 2B illustrate LiF andMetal-F material, other types of materials are possible as well, asexplained above. For example, lithium fluoride may be substituted by alithium fluoride and lithium sulfide combination. In such example, themetal fluoride may be substituted by a metal fluoride/sulfidecombination.

Cathode Active Component—Lithium Metal Compound Component

In another version of the devices, at some point in the state of chargeof the electrode, the cathode includes an active component that includesa lithium metal compound component. Generally the lithium metal compoundcomponent is any compound that includes lithium, a non-lithium metal andan anion and that upon charging of the device yields lithium ions thatmigrate to the anode and a metal compound.

In one version such reaction may be written asLi_(d)M_(e)X_(f)

d Li⁺+de⁻+M_(e)X_(f)

dLi+M_(e)X_(f)  (2)

The left hand side of equation 2 represents the cathode active materialsin the discharged state, where the cathode active component comprises alithium metal component, Li_(d)M_(e)X_(f) and the right hand side ofequation 2 represents the system in the charged state in which thecathode active materials have been converted into the metal compoundcomponent, M_(e)X_(f), and the Li ions are provided for diffusionthrough the electrolyte to the anode and the electrons are provided tothe external circuit. In reaction 2 all of the lithium in the lithiummetal compound is converted to lithium ions. In another version, lessthan all of the lithium in the lithium metal compound is converted tolithium ions. One version of such reaction is given in equation 3Li_(d)M_(e)X_(f)

gLi⁺+ge⁻+Li_(d-g)M_(e)X_(f)  (3)

where g<d. Depending on the thermodynamic and kinetic stability of theLi_(d-g)M_(e)X_(f) compound, such compound may exist asLi_(d-g)M_(e)X_(f) or may disproportionate into a mixture of one or moreof a lithium compound, a metal compound and a lithium metal compound.

In one version the lithium metal compound component is a lithium metaloxide, a lithium metal sulphide, a lithium metal nitride, a lithiummetal phosphide, a lithium metal halide or a lithium metal hydride, ormixtures thereof. In one version the lithium metal compound component isa lithium metal halide. In one version the lithium metal compoundcomponent is a lithium metal fluoride. In one version the lithium metalcompound component is a lithium iron fluoride. In one version thelithium metal compound component is a lithium copper fluoride. In oneversion the lithium metal compound component is a lithium cobaltfluoride.

Cathode Active Component—Metal Component, Lithium Compound Component andLithium Metal Compound Component

In another version of the devices, at some point in the state of chargeof the electrode, the cathode includes an active component that includesa metal component, a lithium compound component and a lithium metalcompound component. The metal component, lithium compound component andlithium metal compound component may be as described above. In versionsof the device, the metal, lithium, metal compound and/or lithiumcompound may have a median characteristic size of 30 nm or less or 20 nmor less or 10 nm or less or 5 nm or less. In some cases, the componentsare intermixed in single particles or layers and within these particlesor layers are separated from one another on the length scales notedand/or exist together in a glassy or amorphous state.

Cathode Active Component—Metal Compound Component

As can be seen from equations 1, 2 and 3 above, in the charged state thecathode active component includes a metal compound component whichincludes a metal and an anion. In one version, the metal compoundcomponent is an oxide, nitride, sulphide, phosphide, halide,sulfur-halide, or hydride of a metal selected from Bi, Ti, V, Cr, Mn,Fe, Co, Ni, Cu, Mo, W and Ru. In one version, the metal compoundcomponent is a fluoride of a metal selected from Bi, Ti, V, Cr, Mn, Fe,Co, Ni, Cu, Mo, W and Ru. In one version, the metal compound componentis a fluoride of a metal selected from Fe, Cu or Co. In one version themetal compound component is FeF₃, FeF₂, CuF₂, CoF₂, or CoF₃. In oneversion the metal compound component is FeF_(x), where x is between 1and 3. In one version the metal compound component is CuF_(x), where xis between 1 and 3. In one version the metal compound component isCoF_(x), where x is between 1 and 3.

Cathode MEIC, Electronic Conductors, and Ionic Conductors

In one version of the devices, the positive electrode includes a mixedelectron-ion conducting component (the “MEIC component”) together withan active component as described above. The MEIC component may generallybe made of any material that is compatible with the other materials ofthe device and allows electron and lithium ion transport sufficient foroperation of the device. In one version, the MEIC component is amaterial having an electronic conductivity of 10⁻⁷S/cm or greater at thedevice operating temperature. In one version, the MEIC component is amaterial having a lithium ion conductivity of 10⁻⁷S/cm or greater at thedevice operating temperature. Examples of materials that may be used asthe MEIC component include, without limitation, lithium titanates,lithium iron phosphates, vanadium oxides, cobalt oxides, manganeseoxides, lithium sulfides, molybdenum sulfides, iron sulfides, LiPON,MoO₃, V₂O₅, carbon, copper oxides, lithium insertion compounds such asLiCoO₂, Li(CoMn)O₂, LiMn₂O₄, Li(CoNiMn)O₂, Li(NiCoAl)O₂, or othermaterials having relatively high lithium ion conductivity. In oneversion, the MEIC component is made of the same material as that of thesolid state electrolyte. In one version, the MEIC component is made of adifferent material than that of the solid state electrolyte. The MEICcomponent may itself possess electrochemical activity (for example MoO₃or V₂O₅) or may not show electrochemical activity (for example LiPON).In one version, the MEIC is LiPON.

If the positive electrode includes an MEIC component, the minimum amountof MEIC component will generally be the amount that allows sufficientlithium ion and electron transport for functioning of the device. Themaximum amount will be that amount of MEIC that provides aelectrochemically active positive electrode material with the requiredspecific capacity or other electrical characteristics when operating atrequired rates, voltage windows, and states of charge. In one version ofthe devices including an MEIC, the minimum amount of MEIC is about 1% byweight of the positive electrode material. In one version of the devicesincluding an MEIC, the minimum amount of MEIC is about 5% by weight ofthe positive electrode material. In one version of the devices includingan MEIC, the maximum amount of MEIC is about 50% by weight of thepositive electrode material. In one version of the devices including anMEIC, the maximum amount of MEIC is about 25% by weight of the positiveelectrode material.

The MEIC material may be provided in the electrode in various forms. Inone example, small particles of MEIC are mixed with theelectrochemically active particles and compressed. In another example,the MEIC coats the active material particles. In yet another example,the MEIC arrays into vertical wires. The MEIC may be comprised of atleast two materials, one having high electron conductivity and anotherhaving high ionic conductivity.

In some versions of the device, the positive electrode includes anelectron conductor dispersed to increase the electron conductivity ofthe electrode. In versions, the component has an electron conductivityabove 10⁻⁷S/cm. This compound may be a carbon or metal compound in someembodiments. Examples of forms of carbon that may be employed includegraphite, activated carbon, nanotubes, nanofibers, nanowires, graphene,graphene oxide, etc. When present, an electron conductor may be presentin an amount of about 20% by weight or less of the active material inthe positive electrode or about 10% by weight or less. As examples, thismaterial may be provided as nanowires, nanoparticles, nanocrystals, andmay be oriented in the direction from the electrode to the electrolyteor may be randomly dispersed. In certain embodiments, the material formsa percolating network throughout the positive electrode.

In some versions of the device, the positive electrode includes a Li⁺ionic conductor dispersed to increase the ion conductivity of theelectrode. As examples, this material may be provided in the form ofnanowires, nanoparticles, nanocrystals, and may be oriented in thedirection from the electrode to the electrolyte or may be randomlydispersed. The ion material may be formed in coatings around the activematerial particles. In certain embodiments, the material forms apercolating network throughout the positive electrode. In certainversions, the material has an ion conductivity of at least 10⁻⁷S/cm atthe operating temperature of the device. In some cases, the material hasan ion conductivity of at least 10⁻⁵S/cm, or the material has an ionconductivity of greater than 10⁴S/cm. Materials with this Li⁺conductivity are known in the art; a non-limiting list includes lithiumiron phosphate, carbon, Li₂O—SiO₂—ZrO₂, Li—Al—Ti—P—O—N, LiMO₂,Li₁₀GeP₂S₁₂, Li_(1.5)Al_(0.5)Ge_(1.5)(PO₄)₃, Li₇La₃Zr₂O₁₂, Li₉SiAlO₈,Li₃Nd₃Te₂O₁₂, Li₅La₃M₂O₁₂(M=Nb,Ta), Li_(5+x)M_(x)La_(3-x)Ta₂O₁₂(M=Ca,Sr,Ba), LiPON, lithium sulfide, lithium iron sulfide, ironsulfide, lithium phosphate, Lisicon, thio-lisicon, glassy structures,lanthanum lithium titanate, garnet structures, β″ alumina, and lithiumsolid electrolytes. In versions, the material has an ion conductivity ofat least greater than the electrolyte. The ion conductor is preferablypresent in amounts of about 20% by weight or less of the active materialin the positive electrode and even more preferably about 10% by weightor less.

Cathode Morphology

In one version of the devices the positive electrode is a thin filmcomprising the active component and, optionally, the MEIC component. Anyactive component and MEIC component described above may be used. Thethin film may be a continuous layer such as one deposited by sputtering.Alternatively, it could be a layer that includes particles and/ornanodomains and is optionally held together by a binder. In one version,the thin film cathode has a thickness of between about 2.5 and 500 nm.In another version the thin film cathode has a thickness of betweenabout 5 and 300 nm. In another version the thin film cathode has athickness of about 200 nm or greater. In some cases, the components ofthe cathode material (the conversion material) are intermixed in singleparticles or layers and within these particles or layers are separatedfrom one another on the length scales noted above and/or exist togetherin a glassy or amorphous state. In some cases, the components areprovided in nanodomains.

According to an embodiment, the cathode contains a first thickness oflithium fluoride material configured in either an amorphous orpolycrystalline state. In addition, the cathode contains a firstplurality of iron metal species nucleated overlying the first thicknessof lithium fluoride material. The cathode also has a second thickness oflithium fluoride material formed overlying the first plurality of ironmetal species. The second thickness of lithium fluoride material isconfigured in either an amorphous or a polycrystalline state to causeformation of a lithiated conversion material. The cathode region may becharacterized by an energy density of greater than 80% to about 100% ofa theoretical energy density of the cathode region. In variousimplementations, the plurality of metal species nucleated overlying thefirst thickness of lithium fluoride material causes formation of exposedregions of the first thickness of lithium fluoride material or a thinnerregion of iron metal species disposed between a pair of the plurality ofiron metal species. For example, each of the first thickness of lithiumfluoride material or the second thickness of lithium fluoride materialcan be characterized by a thickness of 30 nm to 0.2 nm. Each of thefirst plurality of iron metal species can be characterized by a size 5nm to 0.2 nm. The plurality of first iron metal species is spatiallydisposed evenly overlying the thickness of the first thickness oflithium fluoride material.

Cathode Morphology—Metal Compound Particles/Nanodomains

For devices in which the cathode includes a metal compound component andan optional MEIC, in one version the cathode comprises the optional MEICand particles/nanodomains of the metal compound component. The particlesor nanodomains containing the metal compound component may generally beof any shape and size. In one version, at least some of the particles ornanodomains containing the metal component are approximately spherical.However, they may be other shapes as well, such as rods, wires, pillows,polygons, flakes, and combinations of any of these, with or withoutspheres. As used herein, “approximately spherical” means that none ofthe three linear dimensions of the particle has a characteristic lengththat is more than twice the characteristic length of either of the othertwo dimensions. It should be understood that the approximately sphericalparticles or nanodomains described below can be substituted withnon-spherical particles or nanodomains. In such cases, the recited“diameter” may be viewed as a characteristic dimension of the particles,which characteristic dimension is the shortest path across a particle ornanodomain.

In one version, at least some of the particles or nanodomains containingthe metal compound component are approximately spherical and suchparticles have a median diameter of between about 1 and 20 nm. In oneversion, at least some of the particles or nanodomains containing themetal compound component are approximately spherical and such particlesor nanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. The diameter of the particles or nanodomainsmay be measured by methods known to those skilled in the art; methodsinclude visual inspection of SEM and TEM micrographs, dynamic lightscattering, laser diffraction, etc. In one version, metal compoundcomponent comprises particles or nanodomains of iron fluoride. In oneversion, the metal compound component comprises particles or nanodomainsof iron fluoride (ferric fluoride and/or ferrous fluoride) at least someof which are approximately spherical and such spherical particles ornanodomains have a median diameter of between about 1 and 20 nm. In oneversion, the metal compound component comprises particles or nanodomainsof iron fluoride at least some of which are approximately spherical andsuch spherical particles or nanodomains have a median diameter ofbetween about 3 and 10 nm, or between about 1 and 5 nm. In one version,metal compound component comprises particles or nanodomains of copperfluoride. In one version, the metal compound component comprisesparticles or nanodomains of copper fluoride at least some of which areapproximately spherical and such spherical particles or nanodomains havea median diameter of between about 1 and 20 nm. In one version, themetal compound component comprises particles or nanodomains of copperfluoride at least some of which are approximately spherical and suchspherical particles or nanodomains have a median diameter of betweenabout 3 and 10 nm, or between about 1 and 5 nm. In one version, metalcompound component comprises particles or nanodomains of cobaltfluoride. In one version, the metal compound component comprisesparticles or nanodomains of cobalt fluoride at least some of which areapproximately spherical and such spherical particles or nanodomains havea median diameter of between about 1 and 20 nm. In one version, themetal compound component comprises particles or nanodomains of cobaltfluoride at least some of which are approximately spherical and suchspherical particles or nanodomains have a median diameter of betweenabout 3 and 10 nm, or between about 1 and 5 nm. In one version, themetal compound component comprises particles or nanodomains of manganesefluoride at least some of which are approximately spherical and suchspherical particles or nanodomains have a median diameter of betweenabout 1 and 20 nm. In one version, the metal compound componentcomprises particles or nanodomains of manganese fluoride at least someof which are approximately spherical and such spherical particles ornanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In some cases, the components of the cathodematerial (the conversion material) are intermixed in single particles asdescribed herein and within these particles they are separated from oneanother on the length scales noted above and/or exist together in aglassy or amorphous state.

In one version, the cathode comprises an MEIC component and particles ofa metal compound component embedded in a matrix of the MEIC component.The particles or nanodomains of the metal compound component may be asdescribed above.

Cathode Morphology—Metal Particles/Nanodomains and Lithium CompoundParticles/Nanodomains

For devices in which at some state of charge the positive electrodeactive material includes a metal component, a lithium compound componentand an optional MEIC, in one version the positive electrode comprisesthe optional MEIC and particles or nanodomains of the metal componentand particles or nanodomains of the lithium compound component. Theparticles of the metal component and the particles of the lithiumcompound component may generally be of any shape and size. Such activematerial may include some particles or nanodomains containing only metaland other particles or nanodomains containing only lithium compound(rather than particles containing both metal and lithium compound). Inother embodiments, some or all of the particles contain both the metaland lithium compound. Unless stated otherwise herein, the particles maybe either homogeneous (containing only metal, lithium compound or othermaterial) or heterogeneous containing two more materials in a singleparticle (e.g., containing both metal and lithium compound in aparticle). When they are heterogeneous, the components of the cathodematerial (the conversion material) are intermixed in single particlesand within these particles they are separated from one another on thelength scales noted above and/or exist together in a glassy or amorphousstate.

In one version, at least some of the particles or nanodomains of themetal component are approximately spherical. In one version, at leastsome of the particles or nanodomains of the metal component areapproximately spherical and such particles or nanodomains have a mediandiameter of between 1 and 20 nm. In one version, at least some of theparticles or nanodomains of the metal component are approximatelyspherical and such particles or nanodomains have a median diameter ofbetween about 3 and 10 nm. In one version, the metal component comprisesparticles or nanodomains of iron. In one version, the metal componentcomprises particles or nanodomains of iron at least some of which areapproximately spherical and such spherical particles or nanodomains havea median diameter of between about 1 and 20 nm. In one version, themetal component comprises particles or nanodomains of iron at least someof which are approximately spherical and such spherical particles ornanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In one version, the metal component comprisesparticles or nanodomains of copper. In one version, the metal componentcomprises particles or nanodomains of copper at least some of which areapproximately spherical and such spherical particles or nanodomains havea median diameter of between about 1 and 20 nm. In one version, themetal component comprises particles or nanodomains of copper at leastsome of which are approximately spherical and such spherical particlesor nanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In one version, the metal component comprisesparticles or nanodomains of cobalt. In one version, the metal componentcomprises particles or nanodomains of cobalt at least some of which areapproximately spherical and such spherical particles or nanodomains havea median diameter of between about 1 and 20 nm. In one version, themetal component comprises particles or nanodomains of cobalt at leastsome of which are approximately spherical and such spherical particlesor nanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In some embodiments, the metal componentparticles or nanodomains may have other shapes such as rods, wires,pillows, polygons, flakes, and combinations of any of these, with orwithout spheres. Any such particles or nanodomains can possess acharacteristic dimension in the ranges identified here as diameters.

In one version, at least some of the particles or nanodomains of thelithium compound component are approximately spherical. In one version,at least some of the particles or nanodomains of the lithium compoundcomponent are approximately spherical and such particles or nanodomainshave a median diameter of between about 1 and 20 nm. In one version, atleast some of the particles or nanodomains of the lithium compoundcomponent are approximately spherical and such particles or nanodomainshave a median diameter of between about 1 and 10 nm, or between about 1and 5 nm. In one version, the lithium compound component comprisesparticles or nanodomains of lithium fluoride. In one version, thelithium compound component comprises particles or nanodomains of lithiumfluoride at least some of which are approximately spherical and suchspherical particles or nanodomains have a median diameter of betweenabout 1 and 20 nm. In one version, the lithium compound componentcomprises particles or nanodomains of lithium fluoride at least some ofwhich are approximately spherical and such spherical particles ornanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In some embodiments, the lithium compoundparticles or nanodomains may have other shapes such as rods, wires,pillows, polygons, flakes, and combinations of any of these, with orwithout spheres. Any such particles or nanodomains can possess acharacteristic dimension in the ranges identified here as diameters.

In one version, the positive electrode includes an optional MEICcomponent, particles of iron or nanodomains and particles or nanodomainsof lithium fluoride. In one version of this device, at least some of theiron particles or nanodomains are approximately spherical and suchparticles or nanodomains have a median diameter of between about 1 and20 nm. In another version of this device, at least some of the ironparticles or nanodomains are approximately spherical and such particlesor nanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In some of these versions, at least some ofthe lithium fluoride particles or nanodomains are approximatelyspherical and such particles or nanodomains have a median diameter ofbetween about 1 and 20 nm. In some embodiments, the iron and/or lithiumfluoride particles or nanodomains may have other shapes such as rods,wires, pillows, polygons, flakes, and combinations of any of these, withor without spheres. Any such particles or nanodomains can possess acharacteristic dimension in the ranges identified here as diameters.

In one version, the positive electrode includes an optional MEICcomponent, particles or nanodomains of copper and particles ornanodomains of lithium fluoride. In one version of this device, at leastsome of the copper particles or nanodomains are approximately sphericaland such particles or nanodomains have a median diameter of betweenabout 1 and 20 nm. In another version of this device, at least some ofthe copper particles or nanodomains are approximately spherical and suchparticles or nanodomains have a median diameter of between about 3 and10 nm, or between about 1 and 5 nm. In some embodiments, the copperparticles or nanodomains may have other shapes such as rods, wires,pillows, polygons, flakes, and combinations of any of these, with orwithout spheres. Any such particles or nanodomains can possess acharacteristic dimension in the ranges identified here as diameters.

In one version, the positive electrode includes an optional MEICcomponent, particles or nanodomains of cobalt and particles ornanodomains of lithium fluoride. In one version of this device, at leastsome of the cobalt particles or nanodomains are approximately sphericaland such particles or nanodomains have a median diameter of betweenabout 1 and 20 nm. In another version of this device, at least some ofthe cobalt particles or nanodomains are approximately spherical and suchparticles or nanodomains have a median diameter of between about 3 and10 nm, or between about 1 and 5 nm. In some embodiments, the cobaltparticles or nanodomains may have other shapes such as rods, wires,pillows, polygons, flakes, and combinations of any of these, with orwithout spheres. Any such particles or nanodomains can possess acharacteristic dimension in the ranges identified here as diameters.

In one version in which the positive electrode includes a metalcomponent and a lithium compound component and an optional MEICcomponent, the cathode comprises an optional MEIC component andparticles or nanodomains of the metal component embedded in a matrix ofthe lithium compound component. In one version, at least some of theparticles or nanodomains of the metal component are approximatelyspherical. In one version, at least some of the particles or nanodomainsof the metal component are approximately spherical and such particles ornanodomains have a median diameter of between about 1 and 20 nm. In oneversion, at least some of the particles or nanodomains of the metalcomponent are approximately spherical and such particles or nanodomainshave a median diameter of between about 3 and 10 nm, or between about 1and 5 nm. In some embodiments, the metal component particles ornanodomains may have other shapes such as rods, wires, pillows,polygons, flakes, and combinations of any of these, with or withoutspheres. Any such particles or nanodomains can possess a characteristicdimension in the ranges identified here as diameters.

In one version, the positive electrode includes an optional MEICcomponent, particles or nanodomains of iron and a matrix of lithiumfluoride. In one version of this device, at least some of the ironparticles or nanodomains are approximately spherical and such particlesor nanodomains have a median diameter of between about 1 and 20 nm. Inanother version of this device, at least some of the iron particles ornanodomains are approximately spherical and such particles ornanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In some embodiments, the iron particles ornanodomains may have other shapes such as rods, wires, pillows,polygons, flakes, and combinations of any of these, with or withoutspheres. Any such particles or nanodomains can possess a characteristicdimension in the ranges identified here as diameters.

In one version, the positive electrode includes an optional MEICcomponent, particles or nanodomains of copper and a matrix of lithiumfluoride. In one version of this device, at least some of the copperparticles or nanodomains are approximately spherical and such particlesor nanodomains have a median diameter of between about 1 and 20 nm. Inanother version of this device, at least some of the copper particles ornanodomains are approximately spherical and such particles ornanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In some embodiments, the copper particles ornanodomains may have other shapes such as rods, wires, pillows,polygons, flakes, and combinations of any of these, with or withoutspheres. Any such particles or nanodomains can possess a characteristicdimension in the ranges identified here as diameters.

In one version, the positive electrode includes an optional MEICcomponent, particles or nanodomains of cobalt and a matrix of lithiumfluoride. In one version of this device, at least some of the cobaltparticles or nanodomains are approximately spherical and such particlesor nanodomains have a median diameter of between about 1 and 20 nm. Inanother version of this device, at least some of the cobalt particles ornanodomains are approximately spherical and such particles ornanodomains have a median diameter of between about 3 and 10 nm, orbetween about 1 and 5 nm. In some embodiments, the cobalt particles ornanodomains may have other shapes such as rods, wires, pillows,polygons, flakes, and combinations of any of these, with or withoutspheres. Any such particles or nanodomains can possess a characteristicdimension in the ranges identified here as diameters.

In one version in which the positive electrode includes a metal compoundand a lithium compound component and an MEIC component, the cathodecontains particles or nanodomains of the metal compound and the lithiumcompound component embedded in a matrix of the MEIC material. In oneversion, at least some of the particles or nanodomains of the metalcompound and/or at least some particles or nanodomains of the lithiumcompound component are approximately spherical. In one version, at leastsome of the particles or nanodomains of the metal compound and/or thelithium compound are approximately spherical and such particles ornanodomains have a median diameter of between about 1 and 20 nm. In oneversion, at least some of the particles or nanodomains of the metalcompound and/or the lithium compound are approximately spherical andsuch particles or nanodomains have a median diameter of between about 3and 10 nm, or between about 1 and 5 nm. In some embodiments, the metalcompound and/or lithium compound particles or nanodomains may have othershapes such as rods, wires, pillows, polygons, flakes, and combinationsof any of these, with or without spheres. Any such particles ornanodomains can possess a characteristic dimension in the rangesidentified here as diameters.

Cathode Morphology—Lithium Metal Compound Particles or Nanodomains

For devices in which at some state of charge the positive electrodeincludes a lithium metal compound component and an optional MEIC, in oneversion the electrode includes the optional MEIC and particles ornanodomains of the lithium metal compound component. The particles ornanodomains of the lithium metal compound component may generally be ofany shape and size.

In one version, at least some of the particles or nanodomains of thelithium metal compound component are approximately spherical. In oneversion, at least some of the particles or nanodomains of the lithiummetal compound component are approximately spherical and such particlesor nanodomains have a median diameter of between about 1 and 20 nm. Inone version, at least some of the particles or nanodomains of thelithium metal compound component are approximately spherical and suchparticles or nanodomains have a median diameter of between about 3 and10 nm, or between about 1 and 5 nm. In one version, the lithium metalcompound component comprises particles or nanodomains of lithium ironfluoride or lithium copper fluoride or lithium cobalt fluoride. In oneversion, the lithium metal compound component comprises particles ornanodomains of lithium iron fluoride (or lithium copper fluoride orlithium cobalt fluoride) at least some of which are approximatelyspherical and such spherical particles or nanodomains have a mediandiameter of between about 1 and 20 nm. In one version, the lithium metalcompound component comprises particles or nanodomains of lithium ironfluoride (or lithium copper fluoride or lithium cobalt fluoride) atleast some of which are approximately spherical and such sphericalparticles or nanodomains have a median diameter of between about 3 and10 nm, or between about 1 and 5 nm.

Solid State Electrolyte

The solid state electrolyte may generally be made of any material thatis compatible with the other materials of the device, which has alithium ion conductivity large enough to allow passage of lithium ionsfor functioning of the device and has an electronic conductivity smallenough for functioning of the device. In one version the solid stateelectrolyte has a lithium ion conductivity of greater than 10⁻⁷S/cm at100 degrees Celsius. Preferably, the material has an ion conductivity ofat least 10⁻⁵S/cm, and even more preferably the material has an ionconductivity of greater than 10⁻⁴S/cm at 100 degrees Celsius. In oneversion the solid state electrolyte has an electronic conductivity ofless than 10⁻¹⁰S/cm at 100 degrees Celsius. In one version, the solidstate electrolyte is selected from LiPON, lithium aluminum fluoride,Li₂O—SiO₂—ZrO₂, Li—Al—Ti—P—O—N, Li_(3x)La_(2/3-x)TiO₃, Li₁₀GeP₂S₁₂,Li_(1.5)Al_(0.5)Ge_(1.5)(PO₄)₃, Li₇La₃Zr₂O₁₂, Li₉SiAlO₈, Li₃Nd₃Te₂O₁₂,Li₅La₃M₂O₁₂(M=Nb,Ta), Li_(5+x)M_(x)La_(3-x)Ta₂O₁₂ (M=Ca,Sr,Ba), LiPON,lithium phosphate, Lisicon, thio-lisicon, Li₂S—X (X═SiS₂, GeS₂, P₂S₅,B₂S₃, As₂S₃), Li_(a)Al_(b)Ga_(c)B_(d)S_(e)(PO₄)_(f),Li_(a)Al_(b)Ga_(c)B_(d)S_(e)(BO₃)_(f), Li_(a)Ge_(b)Si_(c)S_(d)(PO₄)_(e),Li_(a)Ge_(b)Si_(c)S_(d)(BO₃)_(e), antiperovskite hydrate, glassystructures, lanthanum lithium titanate, garnet structures, β″ alumina,and other lithium solid electrolytes. In one version, the solid stateelectrolyte is LiPON. In one version, the solid state electrolyte is alithium aluminum fluoride. In one version, the solid state electrolyteis LiAlF₄. In certain embodiments, a liquid or gel electrolyte is usedwithout a solid state electrolyte. Such electrolyte may be any of thetypes employed with conventional lithium ion cells.

Anode Material

The negative electrode may generally be made of any material that iscompatible with the other materials of the device and which may storelithium atoms or ions when the device is in the charged state and mayprovide lithium ions for incorporation into the cathode when the deviceis in the discharged state. In one version of the devices the negativeelectrode active material is lithium metal. In one version of thedevices the negative electrode material is a lithium silicide, Li—Sn, orother high capacity, low voltage material that alloys with lithium. Inone version of the devices, the negative electrode active material islithium intercalated into a carbon component, such as graphite. In somecases, the negative electrode active material is a material capable ofinserting lithium ions at a higher reversible capacity than carbon. Suchmaterials include tin, magnesium, germanium, silicon, oxides of thesematerials and the like.

In one version of the devices, the negative electrode material is aporous material that allows lithium plating into the pores, therebyrelieving the swelling stress that would otherwise result on theelectrolyte by anode swelling as a result of lithium plating. In oneversion, the pores are carbon nanotubes, carbon buckyballs, carbonfibers, activated carbon, graphite, porous silicon, aerogels, zeolites,xerogels, etc.

In one version of the devices, the anode is formed in situ during thefirst charge cycle of the battery. In case the device is fabricated inthe discharged state (with a lithiated cathode), the first charge cyclewill extract the lithium from the cathode and deposit it on the anodeside. In the case where the anode is a lithium metal anode, the anode istherefore formed in situ by plating on the anode current collector. Inthis case, preferably, the anode current collector is a metal that doesnot alloy with or react with lithium; a non limiting list of possiblechoices for anode current collector metal includes TaN, TiN, Cu, Fe,stainless steel, steel, W, Ni, Mo, or alloys thereof. In one version,there is an excess of lithium in the device as fabricated on the cathodeside. In another version, there is an excess of lithium in the device asfabricated on the anode side, possibly in the anode current collector.An excess of lithium is desirable to prolong the cycle life of thebattery, as some lithium will inevitably be lost due to side reactions,alloying with current collectors, or in reactions with air and/or waterthat leak into the device.

In one version of the devices, there is an encapsulation thatsubstantially prevents ingress of air and water into the activematerials. The encapsulation may be LiPON, an oxide, nitride,oxynitride, resin, epoxy, polymer, parylene, metals such as Ti or Al, ormultilayer combinations thereof. Moisture and oxygen barriers are knownin food packaging, semiconductor packaging, etc.

Current Collectors

The devices described herein include optional positive and/or negativeelectrode current collectors. The current collectors generally may bemade of any material capable of delivering electrons to the anode or thecathode from the external circuit or delivering electrons to theexternal circuit from the anode and cathode. In one version the currentcollectors are made of a highly electronically conductive material suchas a metal. In one version, the device does not include a cathodecurrent collector and electrons are transferred to and from the cathodedirectly to the external circuit. In one version, the device does notinclude an anode current collector and electrons are transferred to andfrom the anode directly to the external circuit. In one version, thedevice does not include either a cathode current collector or an anodecurrent collector. In one version the negative electrode currentcollector is copper. In one version the negative current collector is acopper alloy. In one version, the negative current collector is copperalloyed with a metal selected from nickel, zinc and aluminum or coppercoated on a metal or polymer foil. In one version the current collectoris copper and also includes a layer of a non-copper metal disposedbetween the copper and the cathode or anode material. In one version thepositive current collector is copper and also includes a layer ofnickel, zinc or aluminum disposed between the copper and the anodematerial. In one version, the positive current collector is aluminum. Inone version, the positive current collector is aluminum or an aluminumalloy. In one version, the positive current collector is aluminum andalso includes a layer of a non-aluminum metal disposed between thealuminum and the cathode or anode material. In one version, the currentcollector is steel or stainless steel. In one version, the currentcollector is steel or stainless steel and also includes a layer of anon-steel metal disposed between the steel and the cathode or anodematerial. The positive electrode current collector and negativeelectrode current collector may be different materials chosen amongthose enumerated above or otherwise.

Energy Density

In one version, a device as described herein has an energy density of atleast about 50 Whr/kg or between about 50 and 1000 Whr/kg when measuredat a temperature of 100 degrees Celsius when cycled between 1 and 4V vs.Li and at a current rate of at least about 200 mAh/g of cathode activematerial. In another version, a device as described herein has an energydensity of between about 100 and 750 Whr/kg. In another version, adevice as described herein has an energy density of between about 250and 650 Whr/kg. In another version, a device as described herein has anenergy density of greater than about 250 Whr/kg. As used herein, energydensity is the energy density at the device level; i.e., the totalenergy stored in the device divided by the mass of the device, where themass of the device includes the mass of the anode, cathode, electrolyte,current collectors and packaging of the device. From a volumetricperspective, in certain embodiments, the device has an energy density ofat least about 600 Wh/L under the conditions set forth above.

In one version, a positive electrode as described herein has anelectrode energy density of between about 500 and 2500 Whr/kg whenmeasured at a temperature of 100 degrees. In another version, a positiveelectrode as described herein has an electrode energy density of betweenabout 800 and 1750 Whr/kg. In another version, a positive electrode asdescribed herein has an energy density of between about 1000 and 1600Whr/kg. In another version, a positive electrode as described herein hasan energy density of greater than about 1000 Whr/kg. As used herein,electrode energy density is the energy density at the electrode level;i.e., the total energy stored in the device divided by the mass of thepositive electrode in the discharged state, where the mass of theelectrode includes the mass of the electrochemically active material,lithium, positive current collector, and any electrochemically inactivecomponents in the cathode such as ion or electron conductor additives.

Mixed Fluoride/Sulfide Cathodes

In one version, at some point in the state of charge, the cathodeincludes a metal component and a lithium compound component containinglithium, fluorine and sulfur. In one version, the lithium compoundcomponent contains a mixture of lithium fluoride and lithium sulfide. Inone version, the lithium compound component contains a lithiumsulfur-fluoride. In one version, the cathode contains lithium, fluorine,sulfur and a metal component selected from iron, copper, cobalt,manganese, bismuth, or alloys of those metals. In one version, thecathode contains compounds including lithium, fluorine, sulfur and iron.In one version, the cathode contains lithium fluoride, lithium sulfideand a metal component selected from iron, copper, cobalt, manganese,bismuth, or alloys of any of these metals. In one version, the cathodecontains lithium fluoride, lithium sulfide and iron. In one version, thecathode contains between about 30 and 80 weight percent lithium fluoride(3LiF+Fe would be 58 wt % LiF), between about 1 and 20 weight percentlithium sulfide and a metal component. In one version, the cathodecontains between about 40 and 70 weight percent lithium fluoride,between about 2 and 15 weight percent lithium sulfide and between about30 and 60 weight percent iron. In one version, the cathode containsbetween about 50 and 70 weight percent lithium fluoride, between about 0and 20 weight percent lithium sulfide and between about 20 and 50 weightpercent iron. In one version, when the electrochemical cell is in arelatively discharged state the cathode contains lithium fluoride,lithium sulfide and a metal component and in a more charged statecontains metal fluoride and lithium sulfide and optional lithiumfluoride and metal components. In such version the cathode in the morecharged state is substantially free of metal sulfide. In one version,when the electrochemical cell is in a relatively discharged state thecathode contains lithium fluoride, lithium sulfide and iron and in amore charged state contains iron fluoride and lithium sulfide andoptional lithium fluoride and iron components. In such version thecathode in the more charged state is substantially free of metalsulfide. In one version, when the electrochemical cell is in arelatively discharged state the cathode contains lithium fluoride,lithium sulfide and a metal component and in a more charged statecontains metal fluoride and metal sulfide and optional lithium fluoridelithium sulfide and metal components. In one version, when theelectrochemical cell is in a relatively discharged state the cathodecontains lithium fluoride, lithium sulfide and iron and in a morecharged state contains iron fluoride and iron sulfide and optionallithium fluoride, lithium sulfide and iron components. In otherversions, the sulfide component may be iron sulfide (FeS or FeS₂), ironsulfate, copper sulfide, lithium sulfide (Li_(x)S), and/or solid sulfur.It has been found that FeS, FeS₂, and Li₂S are significantly betterlithium ion conductors than other oxides known to conduct lithium suchas LiPON, MoO_(x), VO_(x), LiFePO₄, and lithium titanate.

In some implementations, a cell containing a positive electrode with asulfide or other conductivity enhancing agent is cycled in a range wherethe conductivity enhancing agent does not react. Iron sulfide is knownto convert to elemental iron and sulfur at a potential of about 1.7volts versus the lithium/lithium ion couple. It is believed thatelemental sulfur may harm certain solid electrolytes (particularlyoxide-type solid electrolytes), so it may be desirable to preventformation of sulfur during normal cycling. In order to preventelectrochemical reduction of sulfides to form sulfur, the device wouldbe configured through the use of a battery management circuit or othercontrol mechanism to prevent the positive electrode from reaching 1.7volts during discharge. In general, the “cutoff” voltage is chosen sothat the desired electrochemical reaction occurs to completion or nearcompletion (all or most of the electrochemically active material in theelectrode is converted) but the conductivity enhancing component doesnot react. In the case of the iron fluoride—iron sulfide system, adischarge voltage of between about 1.8 and 2.2 volts (e.g., about 2volts) versus the lithium/lithium ion couple is generally suitable. Ironfluoride converts to lithium iron fluoride at about 3 volts and furtherconverts to lithium fluoride and elemental iron at about 2.2 volts.

In certain embodiments, the device includes an interlayer disposedbetween the positive electrode and the electrolyte. Such interlayer mayblock sulfur or other species from migrating to the electrolyte anddamaging it. Therefore, the interlayer should effectively blockdiffusion of sulfur and/or other potentially detrimental species betweenthe electrolyte and the positive electrode. The interlayer should alsoconduct lithium ions and be stable at the cathode operating voltages andversus the cathode materials and the electrolyte materials. Examples ofinterlayer materials and properties are presented herein in the sectionon the cathode/electrolyte interlayer.

In some embodiments, a matrix or other strong binding agent is employedto maintain a conductivity enhancing material and the cathode activematerial in close proximity during repeated cycling. It has beenobserved that the conductivity enhancing material (e.g., iron sulfide)and the cathode active material may segregate over time during normalcycling. If this occurs, then electrode performance suffers. Theconductivity enhancing material should be in close proximity (typicallyin the nanometer scale) to the electrochemically active material. Thisclose proximal relation can be established during manufacture and thenmaintained by use of a matrix during cycling. The matrix is an ionic andelectronic conductor. Examples of suitable matrix materials include LiF,AlF₃, LiAlF₄, SiO₂, Al₂O₃, MoO₃, MoS₂, LiFePO₄, VO_(x), and LiTiO_(x),

In certain versions, the matrix material is provided as a continuouslayer that embeds separate particles or nanodomains of active materialand conductivity enhancing agent. See FIG. 3 for two examples. Forexample, a matrix embeds, when the positive electrode is in thedischarged state, separate particles or nanodomains of (i) iron sulfideand (ii) elemental iron and lithium fluoride. In another example, thematrix embeds, when the positive electrode is in the discharged state,separate particles or nanodomains of (i) iron sulfide (ii) elementaliron, and (iii) lithium fluoride. In some implementations, theconductivity enhancing agent is provided in a core-shell arrangement,with the active material (e.g., iron and/or lithium fluoride) coated bythe conductivity enhancing agent (e.g., iron sulfide). Such core-shellparticles may be embedded in a matrix as described above. In certainversions, the matrix, the active material and the conductivity enhancingagent are provided in the same small particles. As an example, thematrix material may encapsulate two or more small particles ornanodomains, at least one of which is of the active material and atleast another of which of the conductivity enhancing agent. In someimplementations, the composite particle may have a median characteristicdimension of about 5 nm to 100 nm.

Cathode/Electrolyte Interlayer

In one version, the positive electrode in the discharged state containsa metal component and an interlayer disposed between the cathode andelectrolyte, such interlayer being substantially impermeable to themetal component. In some implementations, the interlayer improvescycling performance by preventing migration and/or reaction of thecathode materials with the electrolyte. In one version, the interlayerincludes one or more of the following: lithium fluoride, silica,aluminum phosphate, aluminum fluoride, alumina, and molybdenum oxide. Inone version, the interlayer is lithium fluoride. In one version, theinterlayer is silica. In one version, the positive electrode containsiron and the interlayer is lithium fluoride. In one version, theelectrode contains iron and the interlayer is silica. In one version theinterlayer has a thickness of between about 2 and 50 nm. In one version,the cathode contains iron and the interlayer is lithium fluoride with athickness of between about 2 and 50 nm. In one version, the positiveelectrode contains iron and the interlayer is silica with a thickness ofbetween about 2 and 50 nm. In one version, the electrolyte is LiPON, thepositive electrode contains iron and the interlayer is lithium fluoride.In one version, the positive electrode contains iron and the interlayeris silica. In one version, the positive electrode contains iron and theinterlayer is lithium fluoride with a thickness of between about 2 and50 nm. In one version, the positive electrode contains iron and theinterlayer is silica with a thickness of between about 2 and 50 nm.

Relatively Small Amount of Excess Lithium

Conventional lithium ion cells as fabricated often contain a largeexcess of lithium over what is needed for full charge and discharge ofthe cell. Particularly, solid state and/or thin film lithium ion cellscontain a large excess of lithium over what is needed for full dischargeof the cell. Negative electrodes with large excess lithium will notchange in volume by a large fractional amount. For instance, it iscommon to use 4× excess lithium. In operation, the cell is cycled toonly about 20% of the anode lithium, so the volume change is only 20%.

In one version of the cells described herein there is a relatively smallamount of excess lithium. In one version, there is less than about 25%by weight of excess lithium. Without mitigation, only 25% excess lithiumwould result in negative electrode volume change of about 500%, whichplaces much higher stresses on the electrolyte.

One way to address this challenge is by modifying the electrodestructure(s) to control volume change. Further, a glassy electrolyte maytolerate flexes caused by volumetric changes in the negative electrodeon the order of 100%. In certain embodiments, excess lithium is platedinto open pores, typically in the negative electrode, which relieve theswelling force on the electrolyte. In various embodiments, the poresoccupy the same volume whether they are full of lithium or empty.Therefore, when lithium is plated in the pores, the electrolyte does notexperience any significant stress. Examples of materials that canprovide suitable pores include nanotubes (e.g., carbon nanotubes),carbon buckyballs, carbon fibers, activated carbon, graphite, poroussilicon, aerogels, zeolites, xerogels, and the like.

Another way to address the volumetric expansion associated with limitedexcess lithium in the cell involves using a cell architecture including“multi-stacks” of relatively thinner layers. Each stack includes ananode layer, an electrolyte layer, and a cathode layer. A “one stack”battery (conventional) has all the lithium in one anode of at least50-200 um thickness, and the volume change of that anode would cause a50-200 um swelling, which the cell cannot tolerate. However, if the cellcontains tens (or hundreds, or thousands) of stacks in a single cell,each of which is, e.g., 100s of nm in thickness, the system will bebetter matched between the contraction of the anode to the expansion ofthe cathode, and the electrolyte may be more able to accommodate a flexof 100s of nm than 100s of um. In some examples, a multi-stackconfiguration would use, for instance, 100 layers ofanode/electrolyte/cathode, each layer 1/100^(th) as thick asconventional. An example is presented in FIG. 5 below. This designdelivers the same amount of energy and the same energy density as aconventional cell, but offers distinct advantages. As explained,stresses are better tolerated on the nanoscale than the macroscale. Sohaving 100 anodes change volume by 100 nm each is more stable thanhaving 1 anode change volume by 10 um.

Additionally, lithium reduction in the cell may be facilitated by usingan all solid state system, which significantly reduce or eliminate SEIformation (or more generically, first cycle coulombic inefficiency). TheSEI consumes lithium and as a result, the cell must include excesslithium as fabricated.

In certain embodiments, some or all excess lithium in a cell is providedin the positive electrode as fabricated. In some embodiments, thepositive electrode material has some quantity of elemental lithiumtogether with the other components described above (e.g., metal andlithium compound particles or nanodomains). In some examples, lithiummetal is present in the positive electrode active material at a level ofless than about 50% by weight or less than about 30% by weight.

Space-Charge Effects

In one version, the cathode contains two or more components that havedifferent energies of formation of Frenkel defects or different volumeor areal concentrations of species. At the interface, an exchange ofspecies resulting from the difference of defect formation energy orconcentration causes a space charge layer. In this space charge layer,faster transport of at least one species may result. The species may belithium ions, lithium vacancies, fluorine atoms, fluorine vacancies,metal atoms, or metal vacancies. In one version, the cathode containstwo or more components selected copper fluoride, titanium oxide, lithiumfluoride, cobalt fluoride and iron fluoride. In one version, the cathodecontains copper fluoride and iron fluoride.

In one version, the lithium and/or metal compounds form nanodomains thatimprove charge and/or mass transport. In one version, the transport isimproved via transport at or along grain boundaries. In one version,there may be a space-charge or ion superhighway effect at grainboundaries due to a depletion or enhancement in the vacancy orinterstitial concentration of the diffusing species. See Sata et al,Nature 408 (2000) 946, which is incorporated herein by reference in itsentirety. In a non-limiting example, such an effect is observed at ajunction between LiF and TiO₂, wherein charge transport is improved viaa transfer of Li⁺ that results in an increase of lithium vacancyconductivity in LiF. See Li et al, Nano Lett., 12 (2012) 1241, which isincorporated herein by reference in its entirety. As non-limitingexamples, such a space charge effect may improve the fluorine, lithium,or other atom conductivity at a grain boundary between two materialschosen from: Li, LiF, lithium sulfide, iron, iron fluoride, iron oxide,iron oxyfluoride, bismuth, bismuth fluoride, cobalt, cobalt fluoride,copper oxide, copper sulfide, copper, copper fluoride, aluminum,aluminum fluoride, carbon, carbon fluoride, etc.

Applications for the Devices

The devices described herein may generally be used in any applicationrequiring energy storage. The devices may be particularly well suitedfor in applications such as in electric vehicles, hybrid electricvehicles, consumer electronics, medical electronics, and grid storageand regulation.

Electrode Fabrication Process

The positive electrodes described herein can be fabricated by manydifferent processes. The following is a list of manufacturing options,including methods of material synthesis as well as coating on asubstrate:

-   -   Vacuum processes, including Sputtering, Evaporation, reactive        evaporation, Vapor phase deposition, CVD, PECVD, MOCVD, ALD,        PEALD, MBE, IBAD, and PLD.    -   Wet synthesis, including CBD, Electroplating, Spraying & in situ        formation, Langmuir, Langmuir Blodgett, Layer-by-Layer,        electrostatic spray deposition, ultrasonic spray deposition,        aerosol spray pyrolysis, sol gel synthesis, one pot synthesis,        and other bottom-up methods.    -   Dry synthesis, including pressing, hot pressing, cold pressing,        isostatic pressing, sintering, spark plasma sintering, flame        pyrolysis, combustion synthesis, plasma synthesis, atomization,        and melt spinning    -   Top-down methods such as jet milling, wet/dry milling, planetary        milling, and high energy milling.    -   Coating methods such as slot-die, spin coating, dip coating,        doctor blade, metering rod, slot casting, screen printing,        inkjet printing, aerosol jet, knife-over roll, comma coating,        reverse comma coating, tape casting, slip casting, gravure        coating, and microgravure coating.

Processes that are exclusively material synthesis include sol gelsynthesis, one pot synthesis, bottom-up synthesis, melt spinning.Processes that are exclusively particle size reduction include wetmilling, dry milling, planetary milling, high energy milling, jetmilling. Processes that are exclusively coating include slot-die, spincoating, dip coating, doctor blade, metering rod, slot casting, screenprinting, inkjet printing, aerosol jet, knife-over roll, comma coating,reverse comma coating, tape casting, slip casting, gravure coating,microgravure coating. All other listed processes are some hybrid ofsynthesis/deposition.

Suitable deposition processes include evaporation, vapor phasedeposition, CBD, and slurry coating. Suitable processes for particleformation/downsizing include dry milling, wet milling, high energymilling, or bottom-up chemical synthesis.

In certain embodiments, the positive electrode material is producedusing sputtering, PVD, ALD or CBD. In one method described herein, thedevices are fabricated by sputtering using an Endura 5500, 200 mm byApplied Materials of San Jose Calif. In one version, the devices arefabricated by sequential deposition of the anode current collector,anode, electrolyte, cathode, and cathode current collector on asubstrate. In one version, there is no separate substrate and the anode,electrolyte, cathode, and cathode current collector are depositeddirectly on the anode current collector. In one version, there is noseparate substrate and the cathode, electrolyte, anode, and anodecurrent collector are deposited directly on the cathode currentcollector.

An example fabrication sequence follows. Starting with a substrate suchas a silicon wafer, the process sputters a current collecting layer suchas Cu, Al, Ni, W, Ti, TiN, Ta, TaN, or Mo. Using RF or DC sputtering,deposit alternating layers of 3.5 nm LiF and 0.5 nm Fe, both in an argonenvironment. As one skilled in the art will appreciate, nanostructureswill self-form due to the material interfacial energy. Sputtering ofalternating layers is done without exposure to the atmosphere betweeneach step. The total thickness of the stack defines the cathodecapacity.

Without exposure to atmosphere (particularly water and oxygen), transferthe wafer to a vacuum chamber to sputter LiPON or other solid phaseelectrolyte. LiPON sputtering is known to those skilled in the art. As anon-limiting example of process conditions, use RF sputtering in anitrogen plasma at 15 sccm flow rate, 0.01 torr pressure, and 250 wattspower over a Li₃PO₄ target of 3 in diameter. The LiPON, LiF, and Fedepositions may be shadow-masked so that an area of the bottom currentcollector is exposed for the electrical test.

FIGS. 4A-D are simplified diagrams illustrating a process for forming abattery cell according to an embodiment. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. It is to be appreciated that various steps describedbelow can be added, removed, modified, replaced, re-arranged, repeated,and/or overlapped.

As shown in FIG. 4A, a contact layer 402 is formed on the silicon wafer401. According to an embodiment, battery cells are constructed bysputtering 30 nm Ti and 40 nm TiN on a Si wafer. The Ti and TiN materialare used to provide electrical contacts. Depending on the application,other types of conductive materials (e.g., Cu, Al, etc.) can be used aswell. For example, the thicknesses of the Ti and/or TiN material can bechanged.

The cathode region 403 is formed and overlays the contact layer 402, asshown in FIG. 4B. In certain embodiments, the cathode region 403includes multiple cathode layers and are sputtered onto the contactlayer 402. As described above, the cathode region 403 includesnanostructured conversion materials. In a specific embodiment, thecathode region 403 comprises layers of material that are mixed togetherto form the cathode conversion material. In an implementation, thelayers are created by making sequential layers of Fe and LiF in thethickness ratio of 1:7, which creates a discharged cell withstoichiometry of Fe+6 LiF. For example, the thickness ratio of 1:7 isbased on the stoichiometry of Fe+6 LiF at the discharged state.Depending on the application, other materials may be used to formcathode region 403. In one example, the cathode region 403 includes nlayers of Fe and LiF material: 403 a being a layer of Fe material, 403 bbeing a layer of LiF material, 403 c being a layer of Fe material, andso on. In various embodiments, each cathode layer is very thin (e.g., nothicker than a few nanometers or the size of molecules), which cause thenanostructures of Fe+6LiF to be formed. The sputtering of thin layersfacilitates formation of nanostructures. In a specific embodiment, eachthin cathode layer is no thicker than one or two layer of Fe atoms orLiF molecules. Due to the nanostructure formation, the cathode region issubstantially homogeneous. For example, the nanostructures of Fe+6 LiFform a substantially glassy material. As explained above, as the lengthscale increases, the cathode performance degrades, showing the benefitof nanostructuring cathodes (or cathode particles or nanodomains) downto less than 10 nm. It is to be understood that while Fe and LiFmaterials are deposited one layer at a time, the glassy nanostructuredmaterials formed by the Fe and LiF materials are homogeneous andsubstantially uniform, not layered. Such structures may be created bycodepositing the constituent materials. For example, cosputtering orcoevaporation of Fe and LiF may create a glassy, amorphous mixture of Feand LiF.

Formation of cathode region 403 may require many repeated sputteringprocesses. Once the cathode region 403 is formed, an electrolyte region404 is formed, as shown in FIG. 4C. As explained above, the electrolyteregion may comprises solid-state electrolyte material and/or liquidelectrolyte material. In a specific embodiment, LiPON electrolytematerial with a thickness of about 200 nm is formed and overlays thecathode region 403. It is to be appreciated that other types ofmaterials may be used for electrolyte as well, at different thicknesses.

As shown in FIG. 4D, a lithium foil 405 is provided over the electrolyteregion 404 to define the battery cell region. For example, the lithiumfoil 405 has a thickness of about 100 um, and other thicknesses arepossible as well. Electrical contacts are made to the TiN and Li foilfor measurement on a hot plate maintained at a temperature of about 120°C.

It is to be appreciated that the cathode region 403 with nanostructuredconversion materials can be formed in others ways, in addition to therepeated sputtering process described above. According to variousembodiments, nanostructured cathode conversion materials can be formedusing evaporation processes. For example, materials comprising Fe, Li,and F are evaporated onto the cathode electrical contact layer. In aspecific embodiment, a flash evaporation process is performed to allowthe Fe and LiF material to evaporate quickly and form substantiallyuniform and nanostructured cathode conversion material.

In certain embodiments, a conversion material for a cathode is preparedusing a process in which one or more precursors or reactants arecontacted in solid phase. Many such processes may be used. Collectivelythey are referred to as solid phase synthesis. Examples include hotpressing, cold pressing, isostatic pressing, sintering, calcining, sparkplasma sintering, flame pyrolysis, combustion synthesis, plasmasynthesis, atomization, and melt spinning. Some solid phase synthesesinvolve grinding and mixing of bulk precursor materials. The bulkmaterials are ground to very small dimensions and then combined orotherwise mixed and reacted as necessary to form the desiredcomposition. Milling may be performed via jet milling, cryo milling,planetary milling (Netzsch, Fritsch), high energy milling (Spex), andother milling techniques known to those skilled in the art. In someembodiments, the ground and mixed particles are calcined. In certainembodiments, the grinding apparatus produces particles or nanodomainshaving median characteristic dimensions on the order of about 20 nm orless. An examples of solid phase synthesis processes for producing ironfluoride conversion materials are set forth in U.S. Provisional PatentApplication No. 61/814,821, filed Apr. 23, 2013, and titled“NANOSTRUCTURED MATERIALS FOR ELECTROCHEMICAL CONVERSION REACTIONS”,U.S. Provisional Patent Application No. 61/803,802, filed Mar. 21, 2013,and titled “METHOD FOR FORMING IRON FLUORIDE MATERIAL”, both of whichare incorporated herein by reference in its entirety. In variousembodiments, one reactant contains iron and another reactant containsfluorine. For example, one reactant may be an iron compound containingan anion such as nitrate or nitrite and another reactant may be hydrogenfluoride such as ammonium bifluoride.

In a specific embodiment, nanostructured conversion material is formedby atomically mixing precursor materials in their liquid state. Morespecifically, an implementation provides a method forming ananostructured conversion material. The method includes providing afirst precursor material that includes a metal-containing material. Forexample, the metal-containing material includes iron and/or other metalmaterials. A second precursor material is also provided. The secondprecursor material includes an oxidizing anion material, such as afluoride material. The first precursor material and the second precursormaterial are characterized by a tendency of phase separation. Phaseseparating materials have a positive enthalpy of mixing. In their stablestates, phase separating materials segregate to form distinct regionsprimarily composed of each individual material. It is to be appreciatedthat since the two precursor material has a tendency of phaseseparation, it is difficult to manufacture the nanostructured glassyconversion material with the two precursor materials without using theprocesses described according embodiments of the present inventionherein.

In an atomization process, the two precursor materials are melted intotheir respective liquid states and injected into a cooled chamber thatquenches the materials into an unstable or meta-stable state. Forexample, the first precursor material and the second precursor materialhave different melting temperature, and thus can be melted separately ortogether at a temperature above the melting point. Depending on thespecific implementation, the mixing and injection the two precursormaterials can be performed in different sequences. In a specificembodiment, the two precursor materials are placed together as late aspossible in the process prior to injection. While placed together intheir liquid state, the two precursor materials are then injected to acooling chamber through a single nozzle. For example, the nozzle forcesthe two precursor materials into small-sized particles or nanodomains,which allows mixing at an atomic level to occur, and the material isquenched rapidly to “freeze in” the mixed state.

Alternatively, the two precursor materials can be injected separately bytwo or more nozzles into the cooling chamber, and mixing take placessolely within the cooling chamber. At the cooling chamber, the twoprecursor materials are mixed at scale of less than about 20 nm tobecome a formed particle consisting of nanostructured mixture of the twoprecursors. Since the two precursor materials have a tendency to havephase separation, the form particles or nanodomains need to be cooledrapidly to stay in the mixed and nanostructured state. In variousembodiments, the formed particles or nanodomains are cooled a rate ofleast about 100 degrees Kelvin per second. In a specific embodiment, therate of cooling is close to 10,000 degrees Kelvin per second. Forexample, the formed particles or nanodomains are cooled to a roomtemperature and are sufficiently stable in the nanostructured and mixedstate. Cooling may be performed in various ways. In an implementation,cooling is performed by an injected cold inert gas into the coolingchamber. In another implementation, cooling is performed by a coldsurface such as a cold copper drum or anvil. The formed particles ornanodomains are then collected. For example, additional processes areperformed to use the formed particles or nanodomains as conversionmaterial in a battery cell.

It is to be appreciated that the conversion material can be processedusing different techniques, according to various embodiments of thepresent invention. For example, instead of using a cooling chamber togenerate formed particles or nanodomains, a cooling surface can be used.In a specific embodiment, a spinning cooling surface is provided, andthe formed particle or nanodomain is quickly cooled as a result ofdirect contact to the cooling surface.

As mentioned, nanostructured conversion materials may be formed byevaporation processes. In many evaporation techniques, a precursormaterial is heated to a temperature at which it has a significant vaporpressure and then allowed to deposit on a substrate to a nanoscalethickness. Such techniques include thermal evaporation, e-beamevaporation, vapor phase deposition, close-space sublimation, etc.Depending on the application, precursor material(s) may or may not havea tendency to have phase separation. In their respective vapor state,the two precursor materials are mixed in a chamber to form a mixedmaterial within the chamber, and the mixed material is characterized bya length scale of less than about 20 nm. Cooling may take placenaturally or by contact with a cold surface or cold gas. The mixedmaterial is then collected.

To deposit an iron fluoride compound as described herein, co-evaporationof iron and fluorine containing material may be performed so that thetwo principal components of the material mix in the gas phase beforethey are deposited on the substrate to form nanodomains or particleshaving a length scale of about 20 nm or less. In another embodiment,sources of each of the individual components of the composition areseparately of evaporated and deposited onto the substrate so that thecomponents form distinct layers. By maintaining these layers atsufficiently thin dimensions, and in appropriate mass ratios, thedesired compound is formed. Typically, each layer is quite thin,typically on the order of a nanometer or smaller. The mass ratios arechosen to produce an active compound or mixture having the molar ratiosor stoichiometries set forth elsewhere herein.

One example of a suitable evaporation technique is vapor transportdeposition or flash evaporation. It provides continuous deposition ofthe desired film material by saturating a carrier gas with a vapor froma subliming source. The saturated mixture is directed over a substrateat a relatively low temperature, resulting in a supersaturationcondition and subsequent film growth. In one implementation, a reactoremploys a separate powder source for fluorine and iron. A helium sourceblows heated helium into the powders which are sublimated andtransported into the reactor where, in the vapor phase, the componentsmix before being deposited on a cold substrate. In an appropriatelydesigned apparatus, each of the powders is provided via a separate tube,and during transport through the tube, the powder is vaporized by thehot helium or other carrier gas. A non-limiting list of evaporationsources may include LiF, FeF3, FeF2, LiFeF3, Fe, and Li. The evaporatedsource material may be exposed to a reactive process in an ambient gasor plasma produced by a fluorine-containing material such as F₂, CF₄,SF₆, NF₃, etc. Appropriate precursors for an FeLi_(a)F_(b) compound mayinclude iron nanoparticles, iron (II) fluoride, iron (III) fluoride,stainless steel, lithium metal, lithium fluoride, or vapor phaseprecursors such as F₂, CF₄, SF₆, and NF₃.

In certain embodiments, a positive electrode and associated half-cellmay be prepared by the following process:

Mix 5 wt % superP carbon, 5 wt % PVDF binder, with balance 90 wt %comprised of 3 mol % LiN and 1 mol % FeF₃. Mix that powder with 4× byweight of NMP, and add 1% of a surfactant such as oleic acid oroleylamine Mill via high energy milling (Spex 8000M) in a hardenedstainless steel vial with hardened stainless steel balls for 1 hour, orwet milling (Fritsch Pulverisette 7 or Netzsch microcer) in a ceramicvial with a ceramic agitator and yttria-stabilized zirconia beads of 0.1mm or smaller for 4 hours. Coat that mixture on a Cu or Al foil viamicrogravure or capillary coating to create a wet coating of 1 um. Dryin an inert environment until the solvent is evaporated. Transferwithout exposure to atmosphere to a vacuum chamber to deposit anelectrolyte via sputtering or evaporation of Li₃PO₄. To test in ahalf-cell format, transfer the wafer to an inert environment, press 100um thick Li foil on top, press a stainless steel disk on the Li foil,and contact the stainless steel disk with one electrode and the bottomfoil underneath with the other electrode. Test the wafer at 100° C. inan oven or on a hotplate by performing a galvanostatic test between 1Vand 4V.

Cell Construction

The above disclosure describes various elements of a battery includingcurrent collectors, anodes, cathodes, and electrolytes. Conventionalformat battery designs may be employed. These include both cylindricaland prismatic configurations such as those employed in consumerelectronics, electric vehicles, medical devices, uninterruptible powersupplies, etc. The size and footprint of these batteries may be similarto those of conventional format batteries such as A, AA, AAA, C, 18650,etc.

While the specification has focused primarily on solid stateelectrolytes, it should be understood that the positive electrodesdisclosed herein may be employed in batteries using liquid and gelelectrolytes as well.

FIG. 5 presents an example of a small multi-stack battery configuration.While the depicted device shows only two anodes 503 and two cathodes505, the concept is readily extendable to designs having more, and oftenmany anodes and cathodes; for instance 100 layers ofanode/electrolyte/cathode, each layer on the order of a 100 nm thick.

The anodes 503, cathodes 505, and electrolyte 507 may have compositions,properties, and/or morphologies disclosed above.

Note that there is a current collector disposed between two layers ofactive material in each electrode. These current collectors (509 and511) are horizontally oriented in the depicted embodiment. Theseindividual electrode current collectors are electrically connected to abus or vertical current collector (513 and 515) as depicted in thefigure. Solid electrolyte not only separate adjacent anodes and cathodesbut also separates the electrodes from the vertical current collectorsof the opposite polarity.

In various embodiments, the device is provide with a battery maintenanceor battery controller apparatus such as a battery charger and associatedcircuitry for controlling discharge and/or charge parameters such as cutoff voltages, cut off capacities, current, temperature, and the like.

Experimental Results

FIG. 6: A plot of cell performance measured by cathode volumetric energydensity versus the LiF material of small length scale in a laminatestructure. The energy density is measured by galvanostatic dischargebetween 1 to 4V vs. Li at a 10 C rate and 120° C.; all the cells are anequal total thickness (e.g. a cell with length scale 35 nm has twice asmany layers as a cell with length scale 70 nm). Cells are constructed bysputtering 30 nm Ti and 40 nm TiN on a Si wafer, then sputtering thecathode layers, then a 200 nm LiPON electrolyte. Li foil of 100 umthickness is punched out in a circle of 0.3 cm² area and pressed on todefine the cell area. Electrical contacts are made to the TiN and Lifoil for measurement on a hot plate maintained at 120° C.

The laminates are created by making sequential layers of Fe and LiF inthe thickness ratio of 1:7, which creates a discharged cell withstoichiometry ˜Fe+3 LiF. As the length scale increases, the cathodeperformance degrades, showing the benefit of nanostructuring cathodes(or cathode particles) down to less than 10 nm.

A table summarizing the data from FIGS. 7-10 below. It is useful to notethat modest amounts of sulfur in the cathode significantly improves theelectrode's mass loading ability.

3LiF + Fe + 3LiF + Fe + Composition 3LiF + Fe 3LiF + Fe S_(0.14)S_(0.53) Thickness 66 nm 129 nm 134 nm 134 nm Energy retention at 88%58% 83% 106% 10 C. vs 1 C. Voltage hysteresis 0.89 V 0.72 V 0.72 V 0.75V at 1 C. rate Voltage hysteresis 0.91 V 0.92 V 0.88 V 0.61 V at 10 C.rate

FIG. 7: A plot of constant current charge and discharge of a 66 nmcathode of 3LiF+Fe at 120° C. The cell is constructed and measured asabove, at C-rates of 10 C (dotted line) and 1 C (solid line). The energydensity at 10 C is 88% as high as at 1 C, the voltage hysteresis is0.89V at 1 C and 0.91V at 10 C. There is a marked degradation inperformance of a 66 nm cathode of 3LiF+Fe as a function of C-rate.

FIG. 8: A plot of constant current charge and discharge of a 129 nmcathode of 3LiF+Fe at 120° C. The cell is constructed and measured asabove, at C-rates of 10 C (dotted line) and 1 C (solid line). The energydensity at 10 C is 58% as large as that at 1 C, the voltage hysteresisis 0.92V at 10 C and 0.72V at 1 C. The degradation of performance versusrate is even more significant as the cathode becomes thicker, anindication that performance is limited by mass transfer.

FIG. 9: a plot of a constant current discharge of a cell whose cathodeis 134 nm (3LiF+Fe+S_(0.14)). The cell is constructed and measured asabove, at C-rates of 10 C (dotted line) and 1 C (solid line). The energydensity at 10 C is 83% that at 1 C, the voltage hysteresis at 1 C is0.72V and at 10 C is 0.88V. Compared to a cathode of similar thicknessand no sulfur content in FIG. 3, this cathode has much better rateperformance, showing a marked benefit from 2% S content.

FIG. 10: A plot of a constant current discharge of a cell whose cathodeis 134 nm (3LiF+Fe+S_(0.53)). The cell is constructed and measured asabove, at C-rates of 10 C (dotted line) and 1 C (solid line). The dataat 10 C shows a 106% higher energy density than 1 C, a capacity-averagedvoltage hysteresis of 0.61V vs. 0.75V at 1 C, and an energy efficiencyof 74% versus 64% at 1 C. Within the statistical variation, there isvirtually no degradation in performance at 10 C versus 1 C, showing thatthe sulfide loading of 7% has substantially improved the cell masstransport.

As described above, cathode energy density is improved by nanostructuredconversion materials according to embodiments of the present invention.FIG. 11 provides a plot of cell performance measured by cathodevolumetric energy density versus the LiF material length scale in alaminate structure. The energy density is measured by galvanostaticdischarge between 1 to 4V vs. Li at a 10 C rate and 120° C. All themeasured cells, which the plot is based upon, have substantially thesame total thickness (e.g., a cell with length scale 35 nm has twice asmany layers as a cell with length scale 70 nm). As shown in FIG. 11, asthe LiF length scale is less than 40 nm and the Fe length scale is about5 nm, the cathode energy density is about 1500 Wh/L or even greater.When the LiF length scale is less than 20 nm and the Fe length scale isless than about 5 nm, the cathode energy density about 2500 Wh/L orgreater. It is to be appreciated that the high energy density can beachieved due to the nanostructuring of the particles. The nanostructurecan be formed in various ways according to embodiments of the presentinvention, as described below.

FIG. 12 is a plot of cell performance measured by cathode volumetricenergy density versus the Fe material at small length scale in alaminate structure. The energy density is measured by galvanostaticdischarge between 1 to 4V vs. Li at a 10 C rate and 120° C. in a fullcell configuration. For the purpose of the measurement, cells areconstructed by sputtering 50 nm Pt on a Si/SiO₂ wafer, then sputteringthe cathode layers, then a 200 nm LiPON electrolyte. A top electrode ofFe is sputtered on in a defined area, and during charge, Li is platedonto the Fe surface, creating an anode in situ. Electrical contacts aremade to the Pt and Fe for measurement on a hot plate maintained at 120°C. The laminates are created by making sequential layers of Fe and LiF,as described above, in the thickness ratio of 1:3, which creates adischarged cell with stoichiometry ˜Fe+3 LiF. As the length scaleincreases, the cathode performance degrades, showing the benefit ofnanostructuring cathode morphology down to less than 2 nm. Morespecifically, as shown in FIG. 12, the cathode energy density versuslayer structure plot shows that as the length scale decreases, the pervolume energy density increases. The “20×0.5” on the x-axis denotes 20layers of (0.5 nm Fe+1.5 nm LiF), “20×1” denotes 20 layers of (1 nm Fe+3nm LiF), and “10×2” denotes 10 layers of (2 nm Fe+6 nm LiF).

FIG. 13 provides a cross-section view of nanostructured conversionmaterial on a scale of about 5 nm. As can be seen from FIG. 3 describedabove, the ˜5 nm length scale does not perform as well as conversionmaterial nanostructured at a finer scale (the low performance is anindication of less than ideal material structure). For example, theviews shown in FIGS. 13-15 are a part of the cell structure shown inFIGS. 1A and B.

FIG. 14 provides a cross-section view of nanostructured conversionmaterial on a scale of about 2 nm. At a smaller scale in comparison toFIG. 13, the nanostructured conversion material is performs better thanthe microstructure shown in FIG. 13.

FIG. 15 provides a cross-section view of nanostructured conversionmaterial on a scale of about 2 nm.

FIG. 16 is a plot illustrating an example of the benefits ofnanostructuring a conversion material and maintaining uniformity ofcomposition. For example, a model was created to count the number ofreactions within a distance from any given atom. Assuming that areaction such as Li+F+Fe→FeLiF is one step in the multistep FeF3conversion lithiation reaction, this model computes the distances L1 andL2, where L1 is the distance between F and Li, and L2 is the distancebetween F and Fe. As can be seen from the calculation, a greaterfraction of reactions may be completed within a shorter distance whenthe nearly correct stoichiometry of F/Fe=3 and F/Fe=2.5 are considered.This will lead to a battery with higher performance: higher efficiency,greater charge/discharge speed, and higher delivered energy. Therefore,a glassy/amorphous conversion material should be created in a mannerthat keeps near ideal stoichiometry uniformly throughout the material.

FIG. 27 presents theoretical energy density of lithiated conversioncathode materials versus a standard Li anode. The overpotential isassumed to be 0.7V, accounting for the mass transport losses, activationlosses at reasonable voltage, and hysteresis inherent to conversionreactions. FIG. 18 presents theoretical specific energy of lithiatedconversion cathode materials versus the standard Li anode. Again, theoverpotential is assumed to be 0.7V, accounting for the mass transportlosses, activation losses at reasonable voltage, and hysteresis inherentto conversion reactions. The presented values are theoretical values, sofull conversion at the thermodynamic potentials is assumed.

FIG. 19 presents a plot (voltage (measured against a standard lithiumelectrode) versus cathode material active capacity) for the first 5cycles of charge/discharge of a cupric fluoride sample. As shown, thispositive electrode active material demonstrates reversibility, with onlymoderate hysteresis, high average voltage, and near full capacity.

FIG. 20 presents discharge energy for samples containing certaintransition metal alloys used in a conversion material. Specifically, theconversion material compositions were FeCo+LiF, FeMn+LiF, Fe₃Co+LiF, anda control sample, Fe+LiF. The discharge rate was 10 C, and the dischargevoltage limits are 4 to 1V versus a standard lithium metal electrode.The samples had a nominal thickness ratio of 7LiF:1M, where M is themetal, which was an alloy in the non-control cases. In each sample, tenlayers of metal (at the recited compositions) were formed and ten layersof LiF were interleaved between the metal layers. As can be seen, the50% Fe-50% Co and the 50% Fe-50% Mn samples provided particularly highspecific capacities.

In FIG. 21, capacity and hysteresis statistics are provided for thefollowing conversion material samples: FeCo+LiF, FeMn+LiF, Fe₃Co+LiF,and a control sample of Fe+LiF. The samples were discharged at ratesgiven as C/3, 1 C, 10 C in different colors (C/3 in white, 1 C in gray,and 10 C in black), and voltage limits were 4-1V versus a lithium metalelectrode.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. A positive electrode comprising: a currentcollector; and an electrochemically active material in electricalcommunication with the current collector and comprising: in thedischarged state: a metal component having a median characteristiclength scale of between 3 and 10 nm and selected from the groupconsisting of iron, cobalt, manganese, copper, nickel, bismuth, andalloys thereof; and a lithium fluoride compound intermixed with themetal component, wherein substantially all of the lithium fluoridecompound is characterized by an amorphous structure; and in the chargedstate: a metal fluoride component having a median characteristic lengthscale of between 3 and 10 nm and selected from the group consisting ofiron fluoride, cobalt fluoride, manganese fluoride, copper fluoride,nickel fluoride, bismuth fluoride, and combinations thereof, whereinsubstantially all of the metal fluoride component is characterized by anamorphous structure, and wherein the electrochemically active material,when fully charged has a reversible specific capacity of about 350 mAh/gor greater when discharged with lithium ions at a rate of at least 200mA/g.
 2. The positive electrode of claim 1, wherein the positiveelectrode further comprises a mixed ion-electron conductor component,the mixed ion electron conductor component comprising less than about 50percent by weight of the positive electrode.
 3. The positive electrodeof claim 1, wherein the positive electrode further comprises an electronconductor component and an ion conductor component.
 4. The positiveelectrode of claim 2, wherein the mixed ion-electron conductor componentis selected from the group consisting of thio-LISICON, garnet, lithiumsulfide, FeS, FeS₂, copper sulfide, titanium sulfide, Li₂S—P₂S₅, lithiumiron sulfide, Li₂S—SiS₂, Li₂S—SiS₂—LiI, Li₂S—SiS₂—Al₂S₃, Li₂S—SiS₂—GeS₂,Li₂S—SiS₂—P₂S₅, Li₂S—P₂S₅, Li₂S—GeS₂—Ga₂S3, and Li₁₀GeP₂S₁₂.
 5. Thepositive electrode of claim 2, wherein the mixed ion-electron conductorcomponent has a glassy structure.
 6. The positive electrode of claim 1,further comprising MoO₃, MoO₂, MoS₂, V₂O₅, or combinations thereof. 7.The positive electrode of claim 1, wherein the metal component has amedian characteristic length scale of about 5 nm or less.
 8. Thepositive electrode of claim 1, wherein the lithium fluoride compoundcomprises particles or nanodomains having a median characteristic lengthscale of about 5 nm or less.
 9. The positive electrode of claim 1,wherein during a discharge the metal fluoride component and lithium ionsundergo a reaction to produce the metal component and the lithiumfluoride compound.
 10. The positive electrode of claim 1, wherein theelectrochemically active material is provided in a layer having athickness of between about 10 nm and 300 μm.
 11. The positive electrodeof claim 1, wherein the electrochemically active material, when fullycharged, has a specific capacity of about 350 mAh/g or greater whendischarged with lithium ions at the rate of at least 200 mA/g and at atemperature of about 100° C.
 12. The positive electrode of claim 1,wherein the positive electrode exhibits an average voltage hysteresisthat is less than about 1V when cycled between 1V and 4V vs Li at atemperature of 100° C. and charged at a rate of about 200 mAh/g.
 13. Asolid-state energy storage device comprising: an anode; a solid-stateelectrolyte; and a cathode comprising: a current collector; and anelectrochemically active material in electrical communication with thecurrent collector and comprising: in the discharged state: a metalcomponent having a median characteristic length scale of between 3 and10 nm and selected from the group consisting of iron, cobalt, manganese,copper, nickel, bismuth, and alloys thereof; and a lithium fluoridecompound intermixed with the metal component, wherein substantially allof the lithium fluoride compound is characterized by an amorphousstructure; and in the charged state: a metal fluoride component having amedian characteristic length scale of between 3 and 10 nm and selectedfrom the group consisting of iron fluoride, cobalt fluoride, manganesefluoride, copper fluoride, nickel fluoride, bismuth fluoride, andcombinations thereof, wherein substantially all of the metal fluoridecomponent is characterized by an amorphous structure, and wherein theelectrochemically active material has a reversible specific capacity ofabout 350 mAh/g or greater when discharged with lithium ions at a rateof at least 200 mA/g at 50° C. between 1 and 4V versus Li.
 14. Thedevice of claim 13, wherein the cathode further comprises a mixedion-electron conductor component.
 15. The device of claim 13, whereinthe cathode further comprises an electron conductive additive and an ionconductive additive.
 16. The device of claim 13, wherein the metalcomponent has a median characteristic length scale of about 5 nm orless.
 17. The device of claim 13, wherein the electrochemically activematerial has a reversible specific capacity of about 400 mAh/g orgreater when discharged with lithium ions at a rate of at least 200mA/g.
 18. The device of claim 13, wherein the cathode further comprisesMoO₃, MoO₂, MoS₂, V₂O₃, V₂O₅, or combinations thereof.
 19. The device ofclaim 13, wherein the lithium fluoride compound comprises particles ornanodomains having a median characteristic length scale of about 5 nm orless.
 20. The device of claim 13, wherein during a discharge the metalfluoride component and lithium ions undergo a reaction to produce themetal component and the lithium fluoride compound.
 21. The device ofclaim 13, wherein the anode, solid state electrolyte, and cathode,together comprise a stack characterized by a thickness of about 1 μm to10 μm.
 22. The device of claim 13, wherein the device has an averagevoltage hysteresis less than about 1V when cycled at a temperature of100° C. and charged at a rate of about 200 mA/g.